• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.7
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• pp.69-75
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• 2004

An avoidance/guidance problem of an aircraft against moving obstacle is considered in two dimensional space. The aircraft is modelled as a point mass flying with constant speed. The lateral acceleration is assumed the control input. Artificial potential functions are applied to the terminal point and moving obstacles in order that repulsive forces and an attractive force are produced by the obstacles and the terminal point respectively. A real time guidance/avoidance law is proposed by using the potential forces and relative velocity. The guidance law for a logarithm potential function results the well-known proportional navigation law. The avoidance control command is inverse proportional to the time-to-go to the obstacle and turns the aircraft toward the negative direction of the line-of-sight change. The performance of the proposed guidance/avoidance law is verified with simulations.

• KIEE International Transactions on Power Engineering
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• v.2A no.4
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• pp.131-135
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• 2002

This paper describes a new ultra-fast contingency screening algorithm for on-line TSA without time simulation. All machines are represented in a classical model and the stability index is defined as the ratio between acceleration power during a fault and deceleration power after clearing the fault. Critical clustering of machines is done based on the stability index, and the power-angle curve of the critical machines is drawn assuming that the angles of the critical machines increase uniformly, while those of the non-critical ones remain constant. Finally, the critical clearing time (CCT) is computed using the power-angle curve. The proposed algorithm is tested on the KEPCO system comprised of 900-bus and 230-machines. The CCT values computed with the screening algorithm are in good agreement with those computed using the detailed model and the SIME method. The computation time for screening about 270 contingencies is 17 seconds with 1.2 GHz PC.

• Journal of Electrical Engineering and information Science
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• v.2 no.4
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• pp.66-71
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• 1997

The dielectrophoretic(DEP) force acting on a cell in an electric field is experimentally determined. A cell is accelerated by the DEP force in an electric field generated between micro planar electrodes. the position of the cell is measured and the velocity and acceleration of the cell are calculated based on the measured position data. The DE force is determined from the motion equation of a moving cell in suspension. The electrode structure is fabricated by micromachining technology and the height of electrodes is 1 $\mu\textrm{m}$. Radish cell and yeast are used in th experiments. In the case of radish cell, the DEP force increases as voltage or frequency(1MHz∼3MHz) increases. The voltage dependence can be explained that the DEP force increases when ▽│E│$^2$increases. The frequency dependence means that Re[x\ulcorner] of radish cell is maximized in a certain frequency. In the case of yeast, the DEP force increases only as voltage increases. The reason for the voltage dependence is the same with the case of radish. The DEP force increases only as voltage increases. The reason for the voltage dependence is the same with the case of radish. The DEP force on a yeast does not vary when the frequency varies from 1MHz to 3MHz. This result coincides with the fact that the value of calculated Re[x\ulcorner] is constant in the test frequency range.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.12
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• pp.2298-2305
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• 1992

To obtain the convenient solution of the multibody dynamic systems composed of flexible beams, linear finite element technique is adopted and the nodal coordinates are interpolated in the global inertia frame. Mass matrix becomes an extremely simple constant matrix and the force vector also becomes extremely simple because Coriolis acceleration and centrifugal force are not required. And the elastic force is also simply computed from the moving frame attached to the material. To solve the global differential algebraic euation. an ODE technique is adopted after Lagrange multiplier is computed by the accelerated iterative technique, and the time demanding procedures such as Newton-Raphson iterations and decomposition of the big matrix are not required. The accuracy of the present solution is checked by a well-known example problem.

• The Journal of Korea Robotics Society
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• v.2 no.3
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• pp.234-241
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• 2007

Effective tools which can alleviate the complexity and computational load problem in collision-free motion planning for multi-agent system have steadily been demanded in robotics field. To reduce the complexity, the extended collision map (ECM) which adopts decoupled approach and prioritization is already proposed. In ECM, the collision regions which represent the potential collision of robots are calculated using the computational power; the complexity problem is not resolved completely. In this paper, we propose a mathematical analysis of the extended collision map; as a result, we formulate the collision region as an equation with 5-8 variables. For mathematical analysis, we introduce realistic assumptions as follows; the path of each robot can be approximated to a straight line or an arc and every robot moves with uniform velocity or constant acceleration near the intersection between paths. Our result reduces the computational complexity in comparison with the previous result without losing optimality, because we use simple but exact equations of the collision regions. This result can be widely applicable to coordinated multi-agent motion planning.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.6 no.2
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• pp.56-61
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• 1992

This paper is reported on the simulation and test results of a constant flux vector control scheme of an induction motor without any speed detecting eqiupment, in which the adaptive current PWM inverter is used. The rotor speed is estimated form stator voltage, current and parameters of motor, and control algorithm in the system is performed with by micro processor. By comparing the waveform of input current of this system with that of the case with taco-generator, good agreement is observed except small ripple component. Experimental results which are acquired at start up and during acceleration/deceleration are quite similar to those of the simulation results.

• Journal of Electrical Engineering and Technology
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• v.13 no.2
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• pp.659-668
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• 2018

This paper proposes an optimization approach of a grid-connected photovoltaic and wind hybrid energy system including energy storage considering voltage fluctuation in the electricity grid. A techno-economic analysis is carried out in order to minimize the size of hybrid system by considering the benefit-cost. Lithium-ion battery type is used for both managing the electricity selling to the grid and reducing voltage fluctuation. A new technique is developed to limit the voltage perturbation caused by the solar irradiance and the wind speed through determining the state-of-charge of battery for every hour of a day. Improved particle swarm optimization (PSO) methods, referred to as FC-VACPSO which combines Fast Convergence Particle Swarm Optimization (FCPSO) method and Variable Acceleration Coefficient Based Particle Swarm Optimization (VACPSO) method are used to solve the optimization problem. A comparative study has been performed between standard PSO method and PSO based methods to extract the best size with the benefit cost. A sensitivity analysis has been studied for different kinds and costs of batteries, by considering variable and constant state-ofcharge of battery. The simulations, performed under Matlab environment, yield good results using the FC-VACPSO method regarding the convergence and the benefit cost of the hybrid system.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.6
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• pp.907-917
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• 1997

The purpose of this study is to design an anti-sway motion for industrial overhead cranes which transport objects on a horizontal plane by adjusting movements of a trolley motor and a girder motor. The movement of a hoist motor has not been considered at this time since its role was assumed to move objects only vertically, therefore, not to affect the swing motion of objects. The dynamic behavior of the swing motion shows nonlinear characteristics, which makes the design of anti-sway motion controller difficult. First of all, the nonlinear state equation for the motion of industrial overhead cranes has been derived. Then they have been linearized about normal operating states determined by the dynamic characteristics of motor motion-acceleration, constant speed, and deceleration, and deceleration, during transportation. The partial state feedback control algorithm based on this linearized state equation has been developed on order to suppress the swing motion. The simulation results have demonstrated satisfactory performance of the proposed controller.

• Elastomers and Composites
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• v.50 no.4
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• pp.292-296
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• 2015

Biomimetic artificial basilar membrane being a core part of artificial cochlear requires performance evaluation through aging test. To evaluate the aging properties of PVDF piezoelectric membrane used for artificial basilar membrane, its mechanical properties such as tensile strength and elastic modulus and piezoelectric property such as piezoelectric constant were measured. The aging test conditions and acceleration constants were calculated based on Arrhenius model. The changes in tensile strengths and elastic moduli measured were less than 10~20% after aging test equivalent for 10 years. The piezoelectric constants were decreased drastically to 80% of its initial value in the early stage of the aging test and expected to decrease slowly down to 65% over 10 years. The experimental results show the reliability of totally implantable novel artificial cochlear and will contribute its commercialization.

• Smart Structures and Systems
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• v.9 no.2
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• pp.105-125
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• 2012

A modified Pagano method is developed for the three-dimensional (3D) free vibration analysis of simply-supported, multilayered functionally graded material (FGM) circular hollow cylinders with a constant rotational speed with respect to the meridional direction of the cylinders. The material properties of each FGM layer constituting the cylinders are regarded as heterogeneous through the thickness coordinate, and then specified to obey a power-law distribution of the volume fractions of the constituents, and the effects of centrifugal and Coriolis accelerations, as well as the initial hoop stress due to rotation, are considered. The Pagano method, which was developed for the static and dynamic analyses of multilayered composite plates, is modified in that a displacement-based formulation is replaced by a mixed formulation, the complex-valued solutions of the system equations are transferred to the real-valued solutions, a successive approximation method is adopted to extend its application to FGM cylinders, and a propagator matrix method is developed to reduce the time needed for its implementation. These modifications make the Pagano method feasible for multilayered FGM cylinders, and the computation in the implementation is independent of the total number of the layers, thus becoming less time-consuming than usual.