• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.11 s.116
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• pp.1115-1123
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• 2006

Nuclear fuel rods are exposed to axial flow in a reactor, and flow-induced-vibration due to the flow usually causes damage in the fuel rods. Thus a prior knowledge about dynamic behavior of a fuel rod exposed to the flow condition should be provided. This paper shows that dynamic characteristics of a nuclear fuel rod depend on axial flow velocity. Assuming small lateral displacement, the effects of uniform axial flow are investigated. The analytic results show that axial flow generally reduces fuel rod stiffness and raises its damping in normal condition. Also, the critical axial velocities which make the fuel rod behavior unstable were found. That is, solving generalized eigenvalue equation of the fuel rod dynamic system, the eigenvalues with positive real part are detected. Based on the simulation results, on the other hand, it turns out that the ordinary axial flow in nuclear reactors does not affect to stability of a nuclear fuel rod even in the conservative condition.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.25 no.3
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• pp.74-80
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• 2017

As for A rotary wing aircraft, the configuration change about split yaw swaged rod was executed to improve hit treat capability for dealing with a long rod. The purpose of this study was to analyze if or not the quality of the split yaw swaged rod was obtained, and so the flight safety was ensured or not. Buckling analysis, Coupling Thread Strength Analysis, Thermal Stress analysis and Rod Natural Frequency Analysis were executed for structural analysis. The results of the analysis were presented that the split rod had the sufficient margin of safety and so there were no anomalies in the limit load and no failures in the ultimate load. And there were no resonances in result of natural frequency analysis. In conclusion, this study showed that the split yaw swaged rod had structural safety, so flight safety of rotary wing aircraft was secured and there was no problem in aircraft operation. It is certain that the technology of splitting the yaw swage rod will contribute to the operational Safety of the rotary wing aircraft in the future.

• Journal of Korean Neurosurgical Society
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• v.47 no.3
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• pp.221-223
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• 2010

C1 lateral mass and C2 pedicle (C1LM-C2P) fixation is a relatively new technique for atlantoaxial stabilization. Complications from C1LM-C2P fixation have been rarely reported. The authors report unilateral rod migration into the posterior fossa as a rare complication after this posterior C1-C2 stabilization technique. A 23-year-old man suffered severe head trauma and cervical spine injury after vehicle accident. He was unconscious for 2 months and regained consciousness. He underwent C1LM-C2P fixation for stabilization of type II odontoid process fracture described by Harms. The patient recovered without a major complication. Twenty months after operation, brain computed tomogram performed at psychology department for disability evaluation showed rod migration into the right cerebellar hemisphere. The patient had mild occipital headache and dizziness only regarding the misplaced rod. He refused further operation for rod removal. To our knowledge, this complication is the first report regarding rod migration after Harms method. We should be kept in mind the possibility of rod migration, and C1LM-C2P fixation should be performed with meticulous technique and long-term follow-up.

• Journal of Institute of Control, Robotics and Systems
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• v.19 no.7
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• pp.626-632
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• 2013

When a conductive rod is put within rotating axial magnet wheels arranged parallel, three-axial magnetic forces generate on the rod. In some region, the forces has a property of negative stiffness, thus they can be applied to noncontact conveyance of the rod without a control load. Apart from the passive driving, the magnet wheel should be controlled for the rod to be stayed at the still state or be moved in a specified velocity. But, because a control input is just the rotating speed of the magnet wheel, the number of input is less than that of variables to be controlled. It means that levitation force and thrust force increase at the same time for increasing wheel speed, resulting from a strong couple between two forces. Thus, in this paper, a novel method, in which the longitudinal motion of the rod is controlled indirectly by the normal motion of the rod with respect to the wheel center, is introduced to manipulate the rod without mechanical contact on space.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.525-528
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• 2002

The objective of this study is to investigate characteristics of flow by the Rod shape and the choice of the turbulent intensity enhancement section. The Rod was setup vertically to the way of a nozzle exit flow and nozzle diameter is 17mm. Rod height is 5mm and its shapes are square, triangle, and circle. Characteristics of fluid such as velocity vector distribution, kinetic energy, turbulent intensity, and etc. were visualized, observed, and considered at 3 kinds of Re No. such as 2000, 3000, and 4000. The characteristics of flow field were investigated in each case of the distance rate from the nozzle exit to impinging plate(H/B=8, 10). The temperature of water is $20^{\circ}E$ and the measurement region divided by 3 sections(I, II, III). The nozzle diameter is 17mm. As the experimental result by PIV measurement, scale of the vector profile showed a tendency to an unbalance parabola distribution as increasing of the Re No. When the impinging plates such as square, triangle, and circle shape are installed respectively in front of the flow accelerated, rod shape of the highest velocity vector is circle shape and rod shape of the highest turbulent Intensity is square shape.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1298-1301
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• 2003

The purpose of this research is to evaluate the effect of pre-load and fatigue life of the distracted one-level pedicle screw system. A spring, which acted as a substitute of the ligament, was installed in the one-level pedicle screw system before testing. The static and fatigue properties are now being tested, which includes 6mm rod to 6mm screw, 6mm rod to 6.5mm screw and 6.35mm rod to 6.5mm screw, under pre-load. Until now as test data were analyzed, 6mm rod to 6.5mm screw was found to have the best performances of stillness and fatigue lift, while 6mm rod to 6mm screw showed the shortest fatigue life. If the stiffness of screw was bigger than that of rod. the fatigue life was prolonged. The fatigue life of the distracted pedicle screw was proved to be shorter than that of the one-level pedicle screw system. So the fatigue life was shortened because of the effect of the spring on the flexibility and stiffness of the rod. In order to obtain the stability of the pedicle screw, more tests are under doing on this topic.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.4
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• pp.139-145
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• 2007

The motion of single-rod cylinder is typically controlled by the directional control valve. In some case, the hydraulic system should be energized by the man power and at the same time the motion of a cylinder is controlled manually. It may be confusing for a man to do two things at the same time. The solution is to make up the closed hydraulic circuit with the bi-directional pump and single-rod cylinder without using a directional control valve. In the case of single-rod cylinder, the flows at the rod side and head side are so different that several valves should be installed to make the motion of single-rod cylinder possible. The hydraulic system is composed of a bi-directional pump, a single-rod cylinder, pilot operated check valves, a check valve and a counter balance valve for the purpose of actuating the lifter. The characteristics of a suggested system are analysized mathematically and numerically.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.12
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• pp.1948-1952
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• 2012

The paper presents modal testing and analysis in order to obtain the dynamic characteristics of a middle spacer grids of a nuclear fuel rod. A spacer grid is one of the important structural elements supporting nuclear fuel rods. Such a fuel rod can be oscillated by its thermal expansion, neutron irradiation and etc. due to cooling water flow under the operation of a nuclear power plant. When the fuel rod vibrates, fretting wear due to repeated friction motion between the fuel rods and spacer grids can be occurred, and so the fuel rod is damaged. In this paper, through modal analysis and testing, natural frequencies and modes of a middle spacer grid were calculated, and the following conclusions were obtained. Firstly the numerical first-seven natural frequencies for spacer grids of a fuel rod having complicated structures have a small difference within 3.8% with experimental natural frequencies, and so the suitability of simulation results was verified. Secondly, experimental mode shapes for a middle spacer grid of a nuclear fuel rod were verified by obtaining lower non-diagonal terms through MAC(Modal Assurance Criteria), and were confirmed by the simulation modes.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.52 no.8
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• pp.452-461
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• 2003

The reliability and accuracy of the information on control rod position are very important to the reactor safety and the design of the core protection system. A survey on the RSPT(Reed Switch Position Transmitter) type control rod position indicator system and its actual implementation in the existing nuclear power plants in Korea was performed first. The control rod position indicator having the high performance for SMART was developed on the basis of RSPT technology identified through the survey. The arrangement of permanent magnet and reed switches is the most important procedure in the design of control rod position indicator. The hysteresis of reed switches is one of the important factors in a repeat accuracy of control rod position indicator as well. This paper investigates efficiency of the magnetic flux concentrator and the hysteresis using FEM and verified differences in physicals characteristics by comparing the results of FEM and those of the experiment. As a result, it is shown that the characteristics of prototype control rod position indicator have a good agreement with the results of FEM.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.53 no.8
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• pp.426-432
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• 2004

This paper presents a systematic approach of measurement, modeling and analysis of grounding system impedance in the field of lightning protection system and intelligent power equipments. The measurement and analysis system of ground impedance is based on a computer aided technique. The magnitude and phase of ground impedance were determined by the novel measurement and analysis using the revised fall-of-potential method. The ground impedances of the ground rod of 50 m long are considerably dependent on the frequency. The ground impedance is mainly resistive in the frequency range of 3-20 kHz. At higher frequencies, the reactive components of the ground impedances are no longer negligible and the inductance of the ground rod was found to be the core factor deciding the ground impedance. Although the steady-state ground resistance of the ground rod of 50 m was less than that of the ground rod of 10 m, the ground impedances of the ground rod of 50 m over the frequency range of more than 60 kHz were much greater than those of the ground rod of 10 m. Furthermore, the equivalent circuit model based on the measured data was proposed. and the calculated results were in approximately agreement with the measured data.