• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.22 no.1
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• pp.107-111
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• 2013

The gyroscopes have been used as a suitable inertial instrument for the navigation guidance and attitude controls. The accuracy as very sensitive sensor is limited by the lock-in region (dead band) due to the frequency coupling between two counter-propagating waves at low rotation rates. This frequency coupling gives no phase difference, and an angular increment is not detected. This problem can be overcome by mechanically dithering the gyroscope. This paper presents the design method of mechanical dither by the theoretical considerations and the verification of the theoretical equations through FEM applications. As a result, comparing to the past result, the maximum prediction error of resonant frequency was within 3 percent and peak dither rate was within 5 percent. It was found that the theoretical equations can be feasible for the mechanical performance of dither.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.4
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• pp.53-62
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• 2010

This study introduces about development of multi-DOF ultrasonic motor that are composed of a bar-shaped stator and a spherical rotor. The ultrasonic motor is a motor which is operated by vibrations over frequency of 20kHz. The multi-DOF ultrasonic motor will be developed by expanding the basic theory of existing 1-DOF ultrasonic motor. It can generate 3-DOF rotation of the rotor around perpendicular axes using 3 vibration modes of stator. By using finite element methods, the optimal dimension of stator is decided and made the components of stator. When we apply the multi-DOF ultrasonic motor composed of rotor and stator to the driving test system, it will be checked whether the motor can be driven at the direction of 3-DOF or not. And it is proposed how the simulation of square bar shaped multi-DOF ultrasonic motor is accomplished.

• Journal of the Korea Institute of Military Science and Technology
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• v.16 no.5
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• pp.653-658
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• 2013

For towing the new type armored vehicle and maintaining the close support, the armored recovery vehicle(ARV) with winch and crane has been developed. In case of crane, it is mainly used to salvage heavy objects by rotational and vertical motion. Especially, the crane bracket is very important parts due to fixing the ARV's body and rotary joint and preventing the force rotation of crane. Therefore, the crane bracket needs to have an enough strength to endure the high load and it is very important to analyze the stress distribution under loads. In the present work, the experimental and analytical investigation on structural integrity evaluation of crane bracket were carried out. The simulation of three-dimensional finite element method(FEM) was compared with experimental datum. From the numerical results, the FEM simulations corresponded well with th experimental results and the structural safety was confirmed by safety factor.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2004.11a
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• pp.175-185
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• 2004

Rotating disks are used in various machines such as data storage device, gyroscope, circular saw, etc. Transverse vibration of a rotating disk is very important for the performance of these machines. This work proposes a method to suppress transverse vibration of a very flexible rotating disk in non-contacting manner. A system considered in this study is a very flexible rotating disk with a thrust bearing pad which is located underneath the rotating disk. The pressure force generated in the gap between the rotating disk and the thrust pad pushes the rotating disk in the direction of axis of rotation while the centrifugal force and the elastic recovery force push the rotating disk in reverse direction. The balance between these forces suppresses the transverse vibration of the rotating disk. A coupled disk-fluid system is analyzed numerically. The finite element method is used to compute the pressure distribution between the thrust pad and the rotating disk while the finite difference method is used to compute the transverse vibration of a rotating disk. Results show that the transverse vibration of the rotating disk can be suppressed effectively for certain combination of air bearing and operating parameters.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.60 no.2
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• pp.91-93
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• 2011

This paper is presented for the performance of the Fluid Dynamic Bearing(FDB) by the groove design and the tooling condition. Recently, spindle motors which require smaller size, lower sound noise, lower vibration, and higher speed of the rotation have been placed in high value-added products including Digital Lightening Processors(DLP), Hard Disk Drives(HDD), and ODDs. The spindle motors using the sintered porous metal bearing have higher vibration and acoustic noise by dry contact and large tolerance of the bearing parts. The Fluid Dynamic Bearing (FDB) with grooves is appropriate for spindle motors adequate in regards to mechanical vibration and acoustic noise. The paper shows the performance comparisons of between sintered porous metal bearing and FDB, and each FDBs according to the tooling deviations of grooves by the Finite Element Analysis(FEA) of the mechanical field. This paper shows the methods to make the grooves, the groove's depth, and the prototype of the motor with the fluid dynamic bearing. The performance characteristics of the grooves with the FDB are verified by the experimental results.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.6
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• pp.1949-1954
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• 2010

The gyroscopes have been used as a suitable inertial instrument for the navigation guidance and attitude controls. The accuracy as very sensitive sensor is limited by the lock-in region(dead band) due to the frequency coupling between two counter-propagating waves at low rotation rates. This frequency coupling gives no phase difference, and an angular increment is not detected. This problem can be overcome by mechanically dithering the gyroscope. This paper presents the design method of mechanical dither by the theoretical considerations and the verification of the theoretical equations through FEM(Finite Element Method) applications. As a result, the maximum prediction error of resonant frequency and peak dither rate was under 5 percent. The theoretical equations for the mechanical performances of dither can be said to be feasible.

• Preventive Nutrition and Food Science
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• v.20 no.1
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• pp.60-66
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• 2015

The aim of this study was to determine the heat-penetration characteristics using stationary and rotary retorts to manufacture Kimchi soup. Both heat-penetration tests and computer simulation based on mathematical modeling were performed. The sterility was measured at five different positions in the pouch. The results revealed only a small deviation of $F_0$ among the different positions, and the rate of heat transfer was increased by rotation of the retort. The thermal processing of retort-pouched Kimchi soup was analyzed mathematically using a finite-element model, and optimum models for predicting the time course of the temperature and $F_0$ were developed. The mathematical models could accurately predict the actual heat penetration of retort-pouched Kimchi soup. The average deviation of the temperature between the experimental and mathematical predicted model was 2.46% ($R^2=0.975$). The changes in nodal temperature and $F_0$ caused by microbial inactivation in the finite-element model predicted using the NISA program were very similar to that of the experimental data of for the retorted Kimchi soup during sterilization with rotary retorts. The correlation coefficient between the simulation using the NISA program and the experimental data was very high, at 99%.

• Journal of Mechanical Science and Technology
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• v.19 no.11
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• pp.1988-1997
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• 2005

This study is concerned with structural integrity evaluations for the interference-fit flywheels in reactor coolant pumps (RCPs) of nuclear power plants. Stresses in the flywheel due to the shrinkage loads and centrifugal loads at the RCP normal operation speed, design overspeed and joint-release speed are obtained using the finite element method (FEM), where release of the deformation-controlled stresses as a result of structural interactions during rotation is considered. Fracture mechanics evaluations for a series of cracks assumed to exist in the flywheel are conducted, considering ductile (fatigue) and non-ductile fracture, and stress intensity factors are obtained for the cracks using the finite element alternating method (FEAM). From analysis results, it is found that fatigue crack growth rates calculated are negligible for smaller cracks. Meanwhile, the material resistance to non-ductile fracture in terms of the critical stress intensity factor (K$_{IC}$) and the nil-ductility transition reference temperature (RT$_{NDT}$) are governing factors for larger cracks.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.5
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• pp.60-67
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• 2012

In the study, the effect grinding condition on the workpiece arithmetical average roughness(Ra) to 10 steps leading to cutting each section with the spindle rotational speed 8000rpm and feed rate 150mm/min of grinding in GC(green silicon carbide) grinding processing after heat treatment and non heat treatment of SCM415 material. Also the following conclusions were obtained analysis of stress distribution displacement and finite elements method(FEM) on assemble parts with 3+2 axis simultaneous control through grinding and gave a load 11kg on ATC arm both sides gave a load of 11kg. For the centerline average roughness(Ra) in the heat and non-heat treatment work pieces, which were appeared the most favorable in the fifth section were $0.511{\mu}m$ and $0.514{\mu}m$, that were shown in the near the straight line section was the smallest deformation of curve. In addition, the bad surface roughness appeared on the path is too long by changing angle, the more inclined depth of cut, because the chip discharging is not smoothly.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.5
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• pp.329-336
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• 2015

This paper presents a sorting method of mode vectors and natural frequencies about a rotor-journal bearing system. The rotor is solved by the finite element method, the bearing stiffness and damping coefficient are solved by the finite difference method. At any rotation speed section through the eigenvalue analysis of the system, mode vectors and natural frequencies not sorted are confirmed via the Campbell diagram and the MAC(modal assurance criterion). To sort mode vectors and natural frequencies of the section, a mode sorting method is presented through a method of rearranging the MAC of the mode vectors. Finally, the mode vectors and the natural frequencies are sorted by using the presented method, these are verified through the MAC.