• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.11
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• pp.2322-2327
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• 2002

The corrosion degradation characteristics of the 12Cr alloy steel, which is widely used in fossil power plants as a turbine blade material, are evaluated nondestructively by use of the backward radiated Rayleigh surface wave. In order to evaluate corrosion degradation characteristics, we constructed automated system for the backward radiation, and the frequency dependency of the Rayleigh surface wave is investigated indirectly by measuring the angular dependency of the backward radiation of the incident ultrasonic wave in the specimens. The velocity of the surface wave decrease as the increase of the aging time in the backward radiation profile, which seems to result from the increase of the effective degrading layer thickness. And, amplitude of the surface wave increase as the aging time, which seems to result from the increase of the intergranular corrosion. The result observed in this study demonstrates high potential of the backward radiated ultrasound as a tool for the nondestructive evaluation of the corrosion degradation characteristics of the aged materials.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.11
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• pp.2457-2465
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• 2002

Numerical modeling of a nondestructive testing system plays an important role in many aspects of quantitative nondestructive evaluation (QNDE). The ultimate goal of a model is to predict test results for a specific flaw in a material. Thus, in ultrasonic testing, a system model should include the transducer, its radiation pattern, the beam reflection and propagation, and scattering from defects. In this paper attention is focused on the scattering model and the scattered fields by defects are observed by an elastodynamic boundary element method. Flaw types addressed are void-like and crack-like flaws. When transverse ultrasonic waves are obliquely incident on the flaw, the angular distribution of far-field scattered displacements are calculated and presented in the form of A-scan mode. The component signals obtained from each scattering problem are identified and their differences are addressed. The numerical results are also compared with those obtained by high frequency approximate solutions.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.04a
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• pp.357-362
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• 2002

Most of battery industries are growing explosively as a core strategy industry for the development of the semi-conductor, the LCD, and the mobile communication device. In this thesis, dynamic characteristics of the steel can labeling machine on the automatic cell assembly line are studied. Dynamic characteristic analysis consists of dynamic behavior analysis and finite element analysis and is necessary for effective design of machines. In the dynamic behavior analysis, the displacement, velocity, applied force and angular velocity of each components are simulated according to each part. In the FEA, stress analysis, mode analysis, and frequency analysis are performed for each part. The results of these simulations are used for the design specification investigation and compensation for optimal design of cell manufacturing line. Therefore, Virtual Engineering of the steel can labeling machine on the automatic cell assembly line systems are modeled and simulated. 3D motion behavior is visualized under real-operating condition on the computer window. Virtual Prototype make it possible to save time by identifying design problems early in development, cut cost by reducing making hardware prototype, and improve quality by quickly optimizing full-system performance. As the first step of CAE which integrates design, dynamic modeling using ADAMS and FEM analysis using NASTRAN are developed.

• Journal of Power Electronics
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• v.16 no.4
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• pp.1375-1386
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• 2016

To decouple the secondary saliencies in sensorless permanent magnet synchronous machine (PMSM) drives, a repetitive control (RC) in the angle domain is proposed. In this paper, the inductance model of a concentrated windings surface-mounted PMSM (cwSPMSM) with strong secondary saliencies is developed. Due to the secondary saliencies, the estimated position contains harmonic disturbances that are periodic relative to the angular position. Through a transformation from the time domain to the angle domain, these varying frequency disturbances can be treated as constant periodic disturbances. The proposed angle-domain RC is plugged into an existing phase-locked loop (PLL) and utilizes the error of the PLL to generate signals to suppress these periodic disturbances. A stability analysis and parameter design guidelines of the RC are addressed in detail. Finally, the proposed method is carried out on a cwSPMSM drive test-bench. The effectiveness and accuracy are verified by experimental results.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.6
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• pp.1180-1185
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• 2009

Spasticity is a velocity-dependent stretch reflex disorder of the body motor system developing after the injury of the central nervous system, in which certain muscles are continuously contracted involuntarily. Conventional methods such as the modified Ashworth scale, Spasm frequency scale, pendulum test and isokinetic dynamometer had some disadvantages: limitation in discriminating the increase of resistance, immovable and expensive device, not enough study parameters. Therefore, it is necessary to introduce clinically more useful instrument, which can produce objective data and are more convenient on spasticity measurement. Spasticity measuring methods were reviewed and a new measuring instrument was designed and introduced. The new measuring system is a portable spasticity-measurement system, which encompass various scopes of spasticity-related human signals such as electrophysiologic, kinematic and biomechanical data. Our device was designed in order to measure the joint angle, angular velocity, electromyographic signals and force. We suggest that this new system can diagnose the spasticity of the muscles, objectively.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.151-156
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• 1995

This paper presents a methodology for real-time detecting and identifying the runout geometry of an end mill. Cutter runout is a common but undesirable phenomenon in multi-tooth machining such as end-milling process because it introduces variable chip loading to insert which results in a accelerated tool wear,amplification of force variation and hence enlargement vibration amplitude. Form understanding of chip load change kinematics, the analytical sutting force model was formulated as the angular domain convolution of three dynamic cutting force component functions. By virtue of the convolution integration property, the frequency domain expression of the total cutting forces can be given as the algebraic multiplication of the Fourier transforms of the local cutting forces and the chip width density of the cutter. Experimental study are presented to validata the analytical model. This study provides the in-process monitoring and compensation of dynamic cutter runout to improve machining tolerance tolerance and surface quality for industriql application.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.9
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• pp.840-845
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• 2005

A three branches vortical Hall sensor for detecting rotation angle of brushless motor has fabricated. The sensor is constructed three branches of $150{\mu}m$ width and $300{\mu}m$ distance from central electrode to Hall electrode. Each branch has one Hall output and one Hall input. The central electrode acts as common driving input. According to rotation angle change of brushless motor, sensor gives three position signals phase shifted by $120^{\circ}$. The sensitivity of sensor is 200V/A$\cdot$T at magnetic field of 0.1 T and constant driving current of 1mA. It has also showed three sine waves of Hall output voltages with $120^{\circ}$ phase over one motor rotation. The noise can limit sensor's resolution. We have measured sensor's noise characteristics. The detectable minimum magnetic field is $20{\mu}T$ at driving current 1mA, measured frequency 1 kHz and bandwidth$({\Delta}f)$ of 1Hz.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.77.1-77.1
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• 2014

Galactic spiral arms are abundant with interesting gaseous substructures. It has been suggested that arm substructures arise from the wiggle instability (WI) of spiral shocks. While the nature of the WI remained elusive, our recent work without considering magnetic fields shows that the WI is physically originated from the accumulation of potential vorticity (PV) generated by deformed shock fronts. To elucidate the characteristics of the WI in more realistic galactic situations, we extend our previous linear stability analysis of spiral shocks by including magnetic fields. We find that magnetic fields reduce the amount of density compression at shocks, making the shock fronts to move toward the upstream direction. Magnetic tension forces from bent field lines stabilize the WI by prevent the generation of PV. When the spiral-arm forcing is F=5% of the centrifugal force of galaxy rotation, the maximum growth rate of the WI is found to be about 1.0, 0.4, and 0.2 times the orbital angular frequency for the plasma parameter ${\beta}=100$, 10, and 5, respectively. Shocks with ${\beta}=1$ are stable to the WI for F=5%, while becoming still unstable when F=10%.

• 유체기계공업학회:학술대회논문집
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• 2000.12a
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• pp.129-136
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• 2000

Centrifugal fans are widely used and the noise generated by these machines causes one of the most serious problems. In general, the centrifugal fan noise is often dominated by tones at BPF(blade passage frequency) and its higher harmonics. This is a consequence of the strong interaction between the flow discharged from the impeller and the cutoff in the casing. However, only a few researches have been carried out on predicting the noise because of the difficulty in obtaining detailed Information about the flow field and casing effects on noise radiation. The objective of this study is to develop a prediction method for the unsteady flow field and the acoustic pressure field of a centrifugal fan, and to calculate the effects of small vanes that are attached in original impeller - Splitter impeller. We assume that the impeller rotates with a constant angular velocity and the flow field around the impeller is incompressible and inviscid. So, a discrete vortex method (DVM) is used to model the centrifugal fan and to calculate the flow field. The force of each element on the blade is calculated by the unsteady Bernoulli equation. Lowson's method is used to predict the acoustic source. The splitter impeller changes the acoustic characteristics as well as performance. Two-splitter type impeller and splitter impeller which splitter locates in jet region are good for acoustic characteristics.

• Journal of Institute of Control, Robotics and Systems
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• v.14 no.4
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• pp.353-360
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• 2008

The LGP with nanometer structures resulted in enhancement of optical efficiency. Its fundamental mechanism is to recycle the polarized light via one round-trip through QWP(Quarter-Wave Plate) but the maximum efficiency to reach with this method is limited up to 2. To get the larger efficiency than this limited one a LGP with nanometer-patterned grating is suggested. For its optimum design the computer simulation is performed and suggests a grating that the spatial frequency between adjacent patterns is 500nm, its height 250nm, duty cycle 50%, and its cross section is rectangular. On the basis of simulation results the LGP with nanometer-patterned grating is fabricated and its optical properties such as angular intensity distribution and CIE color coordinates are characterized. The angles of transmitted light are nearly the same as the results expected from the generalized Snell's law. Thus the Mathematica code, developed in this experiment, will be applied to designing the optimized LGP. The LGP with nanometer-patterened grating shows the enhancement of transmitted intensity distribution up to 4.9 times.