• 제어로봇시스템학회:학술대회논문집
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• 1991.10a
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• pp.889-893
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• 1991

This paper describe the mathematical model of helicopter rotor, which is suitable for the calculation of trim condition to develop the stability and control. The mathematical model is a nonlinear, total force and moment model of a single main rotor helicopter. The effects of fuselage, tail rotor, horizontal tail, and vertical tail are included. The phase angle and stick displacement are obtained and compared at the trim condition.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.6
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• pp.75-82
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• 2006

Tiltrotor aircraft can fly about twice faster and several times further than conventional helicopters. These aircraft provide advantages preventing compressibility of advancing side and stall of retreating side of blades because they take forward flight with tilting rotor systems. However, they have limit on forward flight speed because of the aeroelastic instability known as whirl flutter. First, the parametric study on the aeroelastic stability of the isolated rotor system has been performed in this paper. And the effects of pitch-link stiffness, gimbal spring constant, and precone angle on the whirl flutter stability of Smart-UAV have been investigated through CAMRAD II analysis.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1997.04a
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• pp.111-121
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• 1997

The stability of a rotor-bearing system supported by swirl-controlled hybrid journal bearing with pair-type angled injection orifices is investigated for improvement of the whirl frequency ratio by allowing effective control of the tangential flow inside the bearing clearance, i.e., by achieving more freedom in controlling strength and direction of the supply tangential flow inside the bearing clearance. It is suggested that the system instability can be improved through the change of bearing dynamic characteristic parameters with the swirl control. The orifice diameter d$_0$ and recess injection angle $\alpha$ along with combinations of swirl/anti-swirl supply pressures and directions (3.0-3.0MPa, 4.0-2.0MPa, 2.0-4.0MPa) are selected for design parameters for swirl-controlled effective factors dependent on journal speeds (3000, 9000, 15000, 21000 rpm). It has been found that the orifice diameter do shows strong effects on effective maneuverability of direct-stiffness and direct damping values, while recess injection angle $\alpha$ results in substantial magnitude and direction of cross-stiffness. Specifically, recess injection parameters which are functions of angle of orifice feeding flow and recess dimensions showed very feasible effect on the stability of swirl-controlled rotor-bearing system.

• Tribology and Lubricants
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• v.13 no.3
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• pp.63-72
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• 1997

The stability of a rotor-bearing system supported by swirl-controlled hybrid journal bearing with pair-type angled injection orifices is investigated for improvement of the whirl frequency ratio by allowing effective control of the tangential flow inside the bearing clearance, i.e., by achieving more freedom in controlling strength and direction of the supply tangential flow inside the bearing clearance. It is suggested that the system instability can be improved through the change of bearing dynamic characteristic parameters with the swirl control. The orifice diameter $d_0$ and recess injection angle $\alpha$ along with combinations of swirl/anti-swirl supply pressures and directions (3.0~3.0 MPa, 4.0~2.0 MPa, 2.0~4.0 MPa) are selected for design parameters for swirl-controlled effective factors dependent on journal speeds (3000, 9000, 15000, 21000 rpm). It has been found that the orifice diameter $d_0$ shows strong effects on effective maneuverability of direct-stiffness and direct damping values, while recess injection angle $\alpha$ results in substantial effects on the magnitude and direction of cross-stiffness. Specifically, recess injection parameters which are functions of angle of orifice feeding flow and recess dimensions showed very feasible effect on the stability control of swirl-controlled rotor-bearing system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.986-992
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• 2014

This research investigates experimentally and numerically the tilting angle, eccentricity ratio, flying height of axial direction, friction torque, and critical mass of the HDD disk-spindle system due to HDD positioning angle. The tilting angle and the eccentricity ratio are the maximum when the HDD positioning angle is $90^{\circ}$ respect to horizontal position because the external force in radial direction and the torque applied to the rotating part are the maximum when the HDD positioning angle is $90^{\circ}$. The flying height increases with the increase of the HDD positioning angle because the direction of gravity applied to the rotating part changes. The friction torque increases with the increase of the HDD positioning angle until it becomes $60^{\circ}$, and decreases with the increase of the HDD positioning angle after it becomes $60^{\circ}$. The stability is the maximum when the HDD positioning angle is $90^{\circ}$.

• 제어로봇시스템학회:학술대회논문집
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• 1992.10a
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• pp.153-158
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• 1992

The purpose of this paper is to calculate the dynamic derivatives of single rotor Helicopter in forward flight. From trim condition, the equation of motion is derived, and we can calculate the dynamic dervatives. The results were compared with flight test data. The phase angle and stick displacement are obtained and compared at the trim condition.

• Journal of Institute of Control, Robotics and Systems
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• v.20 no.11
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• pp.1103-1111
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• 2014

The results of control law design for a tilt-rotor unmanned aerial vehicle that has a nacelle mounted wing extension (WE) are presented in this paper. It consists of a control surface mixer, stability and control augmentation system (SCAS), hold mode for altitude / speed / heading, and a guidance mode for preprogram and point navigation which includes automatic take-off and landing. The conversion corridor and the control moments derivatives between the original tilt-rotor and its variant of the nacelle mounted WE were compared to show the effectiveness of the WE. The nacelle conversion of the original tilt-rotor starts when the airspeed is greater than 30 km/h but its WE variant starts at 0 km/h in order to reduce the drag caused by the high incidence angle of the WE. The stability margins of the inner loop are presented with the optimization approach. The outer loops for the hold mode are designed with trial and error methods with linear and nonlinear simulation. The main control parameter for altitude control of the helicopter mode is thrust command and it is transferred to the pitch attitude command in airplane mode. Otherwise, the control parameter for the speed of the helicopter mode is the pitch attitude command and it is transferred to the thrust command in airplane mode. Therefore the speed and altitude hold mode are coupled to each other and are engaged at the same time when an internal pilot engages any of the altitude or speed hold modes. The nonlinear simulation results of the guidance control for the preprogrammed mode and point navigation are also presented including automatic take-off and landing in order to prove the full control law.

• Journal of Electrical Engineering and Technology
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• v.6 no.4
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• pp.484-492
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• 2011

Power system analyses, which involve the handling of massive data volumes, necessitate the use of effective visualization methods to facilitate analysis and assist the user in obtaining a clear understanding of the present state of the system. This paper introduces an interface that compensates for the limitations of the visualization modules of dynamic security assessment tools, such as PSS/e and TSAT, for power system variables including generator rotor angle and frequency. The compensation is made possible through the automatic provision of dynamic simulation data in visualized and tabular form for better data intuition, thereby considerably reducing the redundant manual operation and time required for data analysis. The interface also determines whether the generators are stable through a generator instability algorithm that scans simulation data and checks for an increase in swing or divergence. The proposed visualization methods are applied to the dynamic simulation results for contingencies in the Korean Electric Power Corporation system, and have been tested by power system researchers to verify the effectiveness of the data visualization interface.

• Proceedings of the KIEE Conference
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• 1999.07c
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• pp.1239-1241
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• 1999

In this paper, we propose real time transient stability assessment and energy margin estimation using fuzzy approximate reasoning. The proposed method used rotor angle, kinetic energy and acceleration power of generators at clearing time as fuzzy input. In order to calculate energy margin in transient energy function (TEF), we obtained controlling unstable equilibrium point (UEP) using mode of disturbance procedure (MOD). The proposed algorithm is tested on 4-machine, 6-bus, 7-line power system to prove of effectiveness.

• KIEE International Transactions on Power Engineering
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• v.4A no.3
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• pp.134-140
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• 2004

This paper presents an improved group of energy functions reflecting generator damping effects for multi-machine power systems by using Center of Inertia (COI) formulation as an extension of the previous work. Since rotor angles at the Stable Equilibrium Point (SEP) of post-fault systems are generally calculated in COI, system transient energy can be found without assumption of infinite or slack bus, which is a crucial drawback of the absolute rotor angle frame approach. The developed energy functions have a structure preserving property with which it is very flexible to incorporate various models of power system components, especially various load and generator models. The proposed damping-reflected energy functions are applied to the Potential Energy Boundary Surface (PEBS) method, one of the direct methods. Numerical simulation of WSCC 9-bus shows that conservativeness of the PEBS method can be considerably reduced.