• 한국유체기계학회 논문집
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• 제10권2호
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• pp.7-15
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• 2007

A numerical procedure for optimizing the shape of three-dimensional channel with V-shaped ribs extruded on both walls has been carried out to enhance the turbulent heat transfer. The response surface based optimization is used as an optimization technique with Reynolds-averaged Wavier-stoked analysis. Shear stress transport (SST) turbulence model is used as a turbulence closure. Computational results for average heat transfer rate show good agreements with experimental data. The objective function is defined as a linear combination of heat transfer and friction loss-related terms with a weighting factor. Three dimensionless variables such as, rib pitch-to-rib height ratio, rib height-to-channel height ratio, and the attack angle of the rib are chosen as design variables. Nineteen training points obtained by D-optimal designs for three design variables construct a reliable response surface. In the sensitivity analysis, it is found that the objective function is most sensitive to the ratio of rib height-to-channel height ratio. And, optimal values of design variables have been obtained in a range of the weighting factor.

• Journal of Biosystems Engineering
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• 제37권1호
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• pp.1-10
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• 2012

Purpose: The most important element of an agricultural helicopter is the rotor blade realizing lift force. In order to improve the performance of the rotor blades, two types (KA152313 and KB203611) of airfoils were designed and compared. Methods: The nose shape of the KB203611 airfoil was 'drooped' and 'sharp' compared to the leading edge of the KA152313 airfoil. The performance of the experimental airfoils was simulated using CFD-ACE program, and lifts were measured in situ using the 'AgroHeli-4G', a prototype helicopter. Results: Simulated lifts of the blade with the KA152313 airfoil showed proper values for a wide range of angles of attack between $14^{\circ}{\sim}18^{\circ}$, while the simulated lift of the KB203611 blade exhibited maximum values near $13^{\circ}{\sim}14^{\circ}$. In the lift measurements, the range of operable angles of attack was a collective pitch angle at the grip (GP) of $12^{\circ}{\sim}18^{\circ}$ for the KA152313 blade. On the other hand, the range of angles of attack for the KB203611 blade was a GP of $12^{\circ}{\sim}14^{\circ}$. Conclusions: The blade of KA152313 performed well over a wide range of AoAs and the blade of KB203611 performed better at low AoAs. In this study, a variative airfoil blade, gradually emerging from grip to tip using the two different airfoils, was suggested.

• International Journal of Aeronautical and Space Sciences
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• 제14권2호
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• pp.152-161
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• 2013

This paper presents a control effectiveness analysis of the hawkmoth Manduca sexta. A multibody dynamic model of the insect that considers the time-varying inertia of two flapping wings is established, based on measurement data from the real hawkmoth. A six-degree-of-freedom (6-DOF) multibody flight dynamics simulation environment is used to analyze the effectiveness of the control variables defined in a wing kinematics function. The aerodynamics from complex wing flapping motions is estimated by a blade element approach, including translational and rotational force coefficients derived from relevant experimental studies. Control characteristics of flight dynamics with respect to the changes of three angular degrees of freedom (stroke positional, feathering, and deviation angle) of the wing kinematics are investigated. Results show that the symmetric (asymmetric) wing kinematics change of each wing only affects the longitudinal (lateral) flight forces and moments, which implies that the longitudinal and lateral flight controls are decoupled. However, there are coupling effects within each plane of motion. In the longitudinal plane, pitch and forward/backward motion controls are coupled; in the lateral plane, roll and side-translation motion controls are coupled.

• 대한기계학회논문집A
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• 제26권8호
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• pp.1545-1551
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• 2002

The optical storage device has recently experienced significant improvement, especially for the aspects of high capacity and fast transfer rate. However, it is necessary to study a new shape of air bearing surface for the rotary type actuator because the optical storage device has the lower access time than that of HDD (Hard Disk Drives). In this study, we proposed the air bearing shape by using SA (Simulated Annealing) algorithm which is very effective to achieve the global optimum instead of many local optimums. The objective of optimization is to minimize the deviation in flying height from a target value 100nm. In addition, the pitch and roll angle should be maintained within the operation limits.

• 한국소음진동공학회논문집
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• 제15권1호
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• pp.39-45
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• 2005

This research develops an experimental method to measure the motion of a FDB spindle system with a 3.5' disk by using three capacitance probes fixed on the xyz-micrometers, and it shows that a FDB spindle system has the whirling, flying and tilting motion. It also shows that the whirling, flying and tilting motion converge very quickly to the steady state at the same time when the rotor reaches the steady-state speed. However, they are quite large even at the steady state when they are compared with the 10nm flying height of a magnetic head. For the FDB spindle system used in this experiment, the whirl radius and the peak-to-peak variation of flying height and tilting angle at the steady-state speed of 7,200rpm are 0.675m, 30nm and $5.758\times10^{-3^{\circ}}$, respectively, so that the radial motion of the FDB spindle system exceeds a track pitch of a 3.5' HDD with 90,000 TPI.

• 한국정밀공학회지
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• 제31권8호
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• pp.665-670
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• 2014

In this paper, characteristics of a tidal current power generation system are analysis using power hardware-in-the-loop simulation (PHILS). A 10 kW motor generator set is connected to the real grid through a fabricated 10 kW back to back converter. A power control scheme is applied to the back to back converter. A 2 MW class tidal current turbine is modeled in real time digital simulator (RTDS). Generating voltage and current from the 10 kW PMSG is applied to a 2 MW class tidal current turbine in the RTDS using PHILS. The PHILS results depict the rotation speed, power coefficient, pitch angle, tip-speed ratio, and output power of tidal current turbine. The PHILS results in this paper can contribute to the increasing reliability and stability of the tidal current turbines connected to the grid using PHILS.

• 제어로봇시스템학회논문지
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• 제15권11호
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• pp.1130-1136
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• 2009

A new control algorithm for the yaw motion control of a unicycle robot has been proposed in this paper. With the increase of life quality, there are various transportation systems such as segway and unicycle robot which provide not only transportation but also amusement. In most of the unicycle robots share the same technology in that the directions of roll and pitch are controlled by the balance controllers, allowing the robots to maintain balance for a long period by continuously moving forward and backward. However, one disadvantage of this technology is that it cannot provide the capability to the robots to avoid obstacles in their path way. This research focuses to provide the yawing function to the unicycle robot and to control the yaw motion to avoid the obstacles as desired. For the control of yawing motion, the yaw angle is adjusted to the inertia generated by the velocity and torque of a yawing motor which is installed in the center axes of the unicycle robot to keep the lateral control simple. Through the real experiments, the effective and robustness of the yawing control algorithm has been demonstrated.

• 전기학회논문지
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• 제60권6호
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• pp.1204-1208
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• 2011

In this study, we proposed the system that calculates the algorithm with an accelerometer signal and detects the fall shock and it's direction. In order to gather the activity patterns of fall status and attach on the subject's body without consciousness, the device needs to be small. With this aim, it is attached on the right side of subject's waist. With roll and pitch angle which represent the activity of upper body, the fall situation is determined and classified into the posture pattern. The impact is calculated by the vector magnitude of accelerometer signal. And in the case of the elderly keep the same posture after fall, it can distinguish the situation whether they can stand by themselves or not. Our experimental results showed that 95% successful detection rate of fall activity with 10 subjects. For further improvement of our system, it is necessary to include tasks-oriented classifying algorithm to diverse fall conditions.

• 한국정보통신학회논문지
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• 제15권12호
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• pp.2705-2711
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• 2011

최근 멀티미디어 기술의 발달, 특히 음향 기술의 급격한 발달과 더불어 고품질 오디오에 대한 요구와 함께보다 현실감 있는 오디오를 재생하기 위한 실감 오디오기술 개발이 요구되고 있다. 이러한 요구를 만족시키기 위해 사용자의 가상현실 및 증강현실에서 실감나는 오디오 효과를 제공해 줄 수 있는 3차원 오디오에 대한 연구가 활발히 진행되고 있다. 본 논문에서는 증강현실에서 좀 더 나은 오디오 기술을 적용하여 실감나는 오디오 효과를 제공해 줄 수 있는 방법을 연구하고자 하였다. 연구한 내용은 가상세계와 실제세계의 현실감을 제공하기 위하여 마커 위에 띄워진 3D 모델의 움직임에 따라서 움직임에 맞는 사운드. 즉, 거리, 각도 등의 변화에 따른 사운드의 크기 및 피치 변화를 줄 수 있도록 하였다.

• 한국항공우주학회지
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• 제41권6호
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• pp.502-508
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• 2013

새로이 개발된 유도키트를 장착한 모의 활공탄에 대하여 지상투하시험을 수행하였다. 사출형 분리장치의 카트리지와 오리피스 조합에 따른 사출력을 측정한 결과, 오리피스 직경이 클수록 사출력이 크게 작용하였으며, 투하된 후 날개 전개장치를 비롯하여 탄의 내부에 탑재된 시험 장치들의 정상 작동을 확인하였다. 또한 영상자료로부터 활공탄의 피치각은 전방과 후방의 사출력 분포 즉 카트리지와 오리피스 조합에 따라 증가 또는 감소하는 것으로 분석되었다.