• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.12
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• pp.988-995
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• 2010

In this study the (Alnico, Sm-Co) bonded magnets were fabricated by mixing the Sm-Co added alnico alloy powders with epoxy resin and binder, appropriately. Also, the hybrid ring magnets of (Alnico, Sm-Co)/Sr-ferrite were fabricated by coupling the Sr-ferrite composite layer with an (Alnico, Sm-Co) magnet. The magnetic properties of (Alnico, Sm-Co) ring magnets were varied with the amount of Sm-Co powders. The addition of Sm-Co powders increased a remanent induction($B_r$) and coercive force($_BH_C$), while decreasing a surface flux density and repulsive distance. The surface flux density and repulsive distance for the (Alnico, Sm-Co) ring magnet increased with a magnetizing voltage up to about 160 V and reached an apparent saturation point. Also, the measurements of temperature and moisture characteristics showed that the surface flux densities of N-S poles and repulsive distance decreased a little within 4% after 10 days passed.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.2069-2070
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• 2011

In this paper, the fault diagnosis for a gearbox of BLDC motor. The stator of BLDC motor consists of coil winding so it is easy to cool down and it also has a high reliability. In addition, it doesn't have a brush so it is less trouble and good in maintenance. Coupling with the motor which is the power sources, the gear has a high power transfer efficiency and various rotation speed. The gear gets a high driving force through deceleration. Thus it has been widely used. The gearbox fault detection area has not attracted much attention from electrical engineering community. A few papers describe gearbox fault based on vibration. Gearbox fault is diagnosed through FFT analysis of current and voltage. Fault characteristic frequency side band detected by calculating fault frequency. A threshold value is suggested by comparing normal peak value with fault peak value using detected fault characteristic frequency side band. Experimental results demonstrate that motor current and voltage signal analysis are viable tools in detecting these gear faults. Lower side band(LSB) is bigger than upper side band(USB) in current FFT. LSB and USB are similar in voltage FFT. Finally, fault diagnosis system that can easily detect flaws is developted for gearbox of BLDC motor.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.869-874
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• 2002

Hermetic rotary compressor is one of the most important components for air conditioning system since it has a great effect on both the performance and the noise and vibration of the system. Noise and vibration of rotary compressor is occurred due to gas pulsation during compression process and unbalanced dynamic force. In order to reduce noise and vibration, It is necessary to identify sources of noise and vibration and effectively control them. Many approaches have been tried to identify noise sources of compressor. However, compressor noise source identification has proven to be difficult since the characteristics of compressor noise are complicated due to the interaction of the compressor parts and gas pulsation. In this work, Statistical Energy Analysis has been used to trace the energy flow in the compressor and identify transmission paths from the noise source to the sound field.

• Computers and Concrete
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• v.22 no.3
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• pp.305-317
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• 2018

Steel reinforced Engineered Cementitious Composite (ECC) components have been proposed for seismic structural applications, for example in coupling beams, infill panels, joints, columns, and flexural members. The development of strain in the steel reinforcement of cementitious components has been shown to vary based on both the steel reinforcement ratio and the applied deformation history. Strain in the steel reinforcement of reinforced ECC components is an important structural response metric because ultimate failure is often by fracture of the steel reinforcement. A recently proposed bond-slip model has been successfully calibrated to cyclically tested reinforced ECC beams wherein the deformation history contained monotonically increasing cycles. This paper reports simulations of two-dimensional finite element models of reinforced ECC beams to determine the appropriateness and significance of altering a phenomenological bond-slip model based on the applied deformation history. The numerical simulations with various values of post-peak bond-slip softening stiffness are compared to experimental results. Varying the post-peak bond-slip softening stiffness had little effect on the cracking patterns and hysteretic response of the reinforced ECC flexural models tested, which consisted of two different steel reinforcement ratios subjected to two different deformation histories. Varying the post-peak bond-slip softening stiffness did, however, affect the magnitude of strain and the length of reinforcing bar that strain-hardened. Overall, a numerical model with a constant bond-slip model represented well various responses in reinforced ECC beams with multiple steel reinforcement ratios subjected to different deformation histories.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.948-951
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• 1996

High-speed/high-accuracy control of robot manipulator becomes more and more stringent because of the external disturbance and nonlinear characteristics. To meet this ends, lots of control strategies were proposed in the past such as the computed torque control, the nonlinear decoupled feedback control, and adaptive control. These control methods need computations of the inverse dynamics and require much computational effort. Recently, a disturbance observer with unmodeled robot dynamics and simple algorithms to motion control have been widely studied. This paper proposes a motor control strategy based on the disturbance observer which estimate the disturbance of each joint from input-output relationship of the actuator and eliminate the estimated disturbance including the torque due to modeling errors, coupling force, nonlinear friction, and so on. To apply the disturbance observer to closedloop system like velocity servo pack, the modified control structure was constructed and shown that it is equivalent to a disturbance observer in open-loop system. Finally, using the proposed approach, simulation and experiments were carried out for a two-degree-of-freedom SCARA type direct drive robot, and show some results to verify the effectiveness of the proposed algorithms.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.9
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• pp.1866-1873
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• 2002

The pipe-cutting machine developed in this study is a portable device used to cut a steel pipe. The machine, which is attached to the steel pipe by magnetic force, is moving around the pip e using four wheels. It also works for straight cutting of a steel plate. For the higher precision and labor time reduction, the automation of a pipe-cutting process is needed. However, it is not easily achieved because of vibrations and the loss of track. It is also found that the problems of the automation arise from the coupling of the functional requirements for the pipe-cutting machine. So, it is very difficult io solve the problems by a conventional design method. To overcome the difficulties the new design process for the pipe-cutting machine is established by axiomatic approach in this paper. Based on the Independence Axiom design process, a new product is designed and manufactured. Finally, it is verified by experiments that the performance of the automatic pipe-cutting machine is improved

• Smart Structures and Systems
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• v.18 no.4
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• pp.683-705
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• 2016

A semi-active algorithm for edgewise vibration control of the spar-type floating offshore wind turbine (SFOWT) blades, nacelle and spar platform is developed in this paper. A tuned mass damper (TMD) is placed in each blade, in the nacelle and on the spar to control the vibrations for these components. A Short Time Fourier Transform algorithm is used for semi-active control of the TMDs. The mathematical formulation of the integrated SFOWT-TMDs system is derived by using Euler-Lagrangian equations. The theoretical model derived is a time-varying system considering the aerodynamic properties of the blade, variable mass and stiffness per unit length, gravity, the interactions among the blades, nacelle, spar, mooring system and the TMDs, the hydrodynamic effects, the restoring moment and the buoyancy force. The aerodynamic loads on the nacelle and the spar due to their coupling with the blades are also considered. The effectiveness of the semi-active TMDs is investigated in the numerical examples where the mooring cable tension, rotor speed and the blade stiffness are varying over time. Except for excessively large strokes of the nacelle TMD, the semi-active algorithm is considerably more effective than the passive one in all cases and its effectiveness is restricted by the low-frequency nature of the nacelle and the spar responses.

• Journal of the Korean Institute of Telematics and Electronics
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• v.24 no.4
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• pp.696-700
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• 1987

Guide modes in a graded index multinmode optical fiber are turned into clad modes when the optical fiber was bended into a perpendicular direction to its optical axes by microbending forces, which causes the loss of the guiding optical power. The theories reported on this microbending power loss can be applied to calculation of the transmission power loss only when the beding period equals to the mode coupling length. In this paper, we obtained the general expression of the optical power transmission loss in a graded index multimode fiber bended periodically. This can be applied to the calculation of the power loss of the periodically microbended fiber with an arbitrary bending shape and period. Also, by using the beam theory in mechanics, we could derive the expression of the displacement of the optical fiber caused by the external force which bends the fiber into a periodic trapezoidal shape. Experiments were carried out to determine the dependence of the power loss on the period of the microbending forces. Experimnetal results were in good agreement (in the same order of the magnitude) with theoritical values derived in our work within the bending period region of 2mm-10mm.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.479-482
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• 2008

In order to more closely examine the vacuum arc phenomena, it is necessary to predict the magnetohydrodynamic (MHD) characteristics by the multidisciplinary numerical modeling, which is coupled with the electromagnetic and hydrodynamic fields, simultaneously. In this study, the thermal-fluid characteristics of high current vacuum arcs were calculated by a commercial multiphysics package, ANSYS, in order to obtain Joule heat, Lorentz force and the interactions with flow variables. We assumed the diffused-mode arc within an AMF vacuum interrupter. It was found with four different currents that the temperature distributions on the anode surface are diffused uniformly without concentration in 7kA for both types (cup and coil-type). But the arc plasma transition and an increase of thermal flux density for increasing the applied current have caused the change of temperature distributions on the anode surface. We should need further studies on the two-way coupling method and radiation model for arc plasmas in order to accomplish the advanced analysis method for multiphysics.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2000.11a
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• pp.99-107
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• 2000

With the results of calculation for natural frequencies, the forced reponses of coupled vibration of propulsion shafting were analysed by the modal analysis method. For the forced response analysis, axial exciting forces, axial damper/detuner, propeller exciting forces and damping coefficients were extensively investigated. As the conclusion of this study, some items are cleared as next. - The torsional amplitudes are not influenced by the radial excitation forces. - The axial vibrational amplitudes are influenced by the tangential exciting forces. An increase of amplitude is observed for the speed range in the neighbourhood of any torsional critical speed. - The coupling effect becomes larger if torsional and axial critical speed are closer together. - The axial exciting force of propeller is relatively strong, comparing with those of axial forces of cylinder gas pressure and oscillating inertia of reciprocating mechanism. Therefore, as a resume one can say, that- Torsional vibration calculation with the classical one dimension model is still valid. - The influence of torsional excitation at each crank upon the axial vibration is impotent, especially in the neighbourhood of a torsional critical speed. That means that the calculation of axial vibration with the classical one dimension model is insufficient in most of cases. - The torsional exciting torque of propeller can be neglected in most of cases. But, the axial exciting forces of propeller can not be neglected for calculating axial vibration of propulsion shafting.