• Proceedings of the Korean Society of Precision Engineering Conference
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• 1994.10a
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• pp.958-968
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• 1994

This paper presents a dynamic analysis of the high-speed spindle system for vertical machining center using finite techniques. The computed natural frequencies are compared with the measured frequencies obtained from experimental modal analysis. The results show that the bending and twisting deformations of the spindle housing dominate in the lowest modes owing to low dynamic stiffness of the housing structure. The design parameters in the analysis are : (a) panel thickness of the housing (b ) height of the housing, and (c) spindle-to-column distance of the housing. Through sensitivity analysis and optimizing simulation considering design constraints, an optimal design of the spindle system has been obtained.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.2
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• pp.146-151
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• 2001

The effects of slant interface in the hybrid specimen on the dynamic crack propagation behavior have been investigated using dynamic photoelasticity. The dynamic photoelasticity with the aid of Cranz-Shardin type high speed camera system is utilized to record the dynamic stress field around the dynamically propagating inclined interface crack tip in the three point bending specimens. The dynamic load is applied by a hammer dropped from 0.08m high without initial velocity. The dynamic crack propagation velocities and dynamic stresses field around the interface crack tips are investigated. Theoretical dynamic isochromatic fringe loops are compared with the experimental reults. It is interesting to note that the crack propagating velocity becomes comparable to the Rayleigh wave speed of the soft material of a specimen when slant angle decreases.

• Korean Journal of Applied Biomechanics
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• v.31 no.3
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• pp.205-213
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• 2021

Objective: The aim of this study was to analyze body stability Joint coordination pattern though as bending stiffness of shoes during stance phase of running. Method: 47 male subjects (Age: 26.33 ± 2.11 years, Height: 177.32 ± 4.31 cm, Weight: 65.8 ± 3.87 kg) participated in this study. All subjects tested wearing the same type of running shoes by classifying bending stiffness (A shoes: 3.2~4.1 N, B shoes: 9.25~10.53 N, C shoes: 20.22~21.59 N). They ran 10 m at 3.3 m/s (SD ±3%) speed, and the speed was monitored by installing a speedometer at 3 m intervals between force plate, and the measured data were analyzed five times. During running, ankle joint, MTP joint, coupling angle, inclination angle (anterior-posterior, medial-lateral) was collected and analyzed. Vector coding methods were used to calculate vector angle of 2 joint couples during running: MTP-Ankle joint frontal plane. All analyses were performed with SPSS 21.0 and for repeated measured ANOVA and Post-hoc was Bonferroni. Results: Results indicated that there was an interaction between three shoes and phases for MTP (Metatarsalphalangeal) joint angle (p = .045), the phases in the three shoes showed difference with heel strike~impact peak (p1) (p = .000), impact peak~active peak (p2) (p = .002), from active peak to half the distance to take-off until take-off (p4) (p = .032) except for active peak~from active peak to half the distance to take-off (p3) (p = .155). ML IA (medial-lateral inclination angle) for C shoes was increased than other shoes. The coupling angle of ankle angle and MTP joint showed that there was significantly difference of p2 (p = .005), p4 (p = .045), and the characteristics of C shoes were that single-joint pattern (ankle-phase, MTP-phase) was shown in each phase. Conclusion: In conclusion, by wearing high bending stiffness shoes, their body instability was increased during running.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2012.06a
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• pp.184-184
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• 2012

Recently, as a result of the application of large and multi-blade propellers with high efficiency for large vessels, the vertical bending stiffness of propulsion shafting system tends to be declined. For some specific vessels, the shaft arrangement leads to the forward stern tube bearing to be omitted, decreasing vertical bending stiffness. In this respect, decreased vertical bending stiffness causes the problem which is the blade order resonance frequency to be placed within the operational range of propulsion shafting system. To verify whirling vibration, the measurement should be carried out covering the range of MCR, however, the range is un-measurable. To resolve the measurement issue, this study shows the measuring method and the estimating method of whiling vibration by using resonance frequency of sub harmonic.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.2
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• pp.55-59
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• 2012

This study performs the bending and contact stress analyses for a pair of mating gears during rotation. The interested gears are used for a railway reducer. In general, the railway reducer needs high speed rotation, which leads to a large gear ratio. Thus, it is not easy to apply finite element method to investigate the strength performance, since the size of a gear is much larger than that of a pinion. In this study, the bending and contact stresses determined from FEM are compared with the values determined from the ISO code.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.10a
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• pp.121-129
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• 1997

Bellows are suggested as energy absorbing elements for automotive steering systems. A metallic bellows has nearly constant axial collapse load which is desirable as an energy absorbing element for a steering column. Axial collapsability and bending flexibility of bellows can be utilized to reduce upward tilting and backward displacement of steering columns in the early stage of high speed crash. Since bending flexibility of bellows has negative effects on the vibration characteristics of steering columns it is necessary to maximize the first natural frequency of a bellows while maintaining its plastic bending flexibility and axial collapse load. An effort is made to attain optimum design of bellows based upon the Taguchi method. A general guideline for design of bellows is suggested.

• Korean Journal of Materials Research
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• v.12 no.4
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• pp.254-258
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• 2002

To realize channel cross-connecting in optical communications systems, a high speed optical matrix switch was fabricated using z-cut $LiNbO_3$. For switch fabrication was design bending structure and coupling length and four $2{\times}2$ directional couplers were integrated on one substrate far construction of a $4{\times}4$ switch. Single-mode optical waveguides were formed by Ti-diffusion at a wet $O_2$ atmosphere. Ti-diffusion profile, refractive index variation and waveguide morphology were analyzed by Prism coupler and optical microscopy, respectively.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.8 s.185
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• pp.154-162
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• 2006

By laying its drum horizontally, front-loaded washing machine mostly used in Europe that uses the head of the water to launder was appropriate for washing only small amount of laundry. However, the demands of customers are requiring front-loaded washing machine to handle big capacity laundry as well, and have faster rotation speed to increase drying ability. To meet such demands, more stress from bending and twisting are complexly loaded onto the shaft supporting the horizontal drum, causing problems in fracture strength and fatigue life. Shafting system is mainly divided into flange and shaft. Flange is located between the drum and shaft, transferring power from the shaft to drum, and acting as a supporter of the back of the drum. Shaft is connected from the flange to insert production, transferring power from the motor to drum, and mainly acting as stiffness against the horizontal weight of the shafting system. In this paper, strength analysis and experiment were executed on both the shaft and flange of front-loaded washing machine to suggest the design improvement of shafting system for big capacity, high-rotation drying. Also, verification of this evaluation was executed on fracture strength and fatigue life for studied shaft system.

• KEPCO Journal on Electric Power and Energy
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• v.7 no.2
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• pp.269-275
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• 2021

The turbine rotor, one of the main facilities in a power plant, it generates electricity while rotating at 3600 RPM. Because it rotates at high speed, it requires careful management because high vibration occurs even if it is deformed by only 0.1mm. However, bending occurs due to various causes during turbine operating. If turbine rotor bending occurs, the power plant must be stopped and repaired. In the past, straightening was carried out using a heating torch and furnace in the field. In case of straightening in this way, it is impossible to proceed systematically, so damage to the turbine rotor may occur and take long period for maintenance. Long maintenance period causes excessive cost, so it is necessary to straighten the rotor by minimizing damage to the rotor in a short period of time. To solve this problem, we developed a turbine rotor straightening equipment using high-frequency induction heating equipment. A straightening was validated for 500MW HIP rotor, and the optimal parameters for straightening were selected. In addition, based on the experimental results, finite element analysis was performed to build a database. Using the database, a straightening amount prediction model available for rotor straightening was developed. Using the developed straightening equipment and straightening prediction model, it is possible to straightening the rotor with minimized damage to the rotor in a short period of time.

• Smart Structures and Systems
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• v.28 no.6
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• pp.827-838
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• 2021

The dynamic displacement is considered to be an important indicator of structural safety, and becomes an indispensable part of Structural Health Monitoring (SHM) system for high-speed railway bridges. This paper proposes an indirect strain based dynamic displacement reconstruction methodology for high-speed railway box girders. For the typical box girders under eccentric train load, the plane section assumption and elementary beam theory is no longer applicable due to the bend-torsion coupling effects. The monitored strain was decoupled into bend and torsion induced strain, pre-trained multi-output support vector regression (M-SVR) model was employed for such decoupling process considering the sensor layout cost and reconstruction accuracy. The decoupled strained based displacement could be reconstructed respectively using box girder plate element analysis and mode superposition principle. For the transformation modal matrix has a significant impact on the reconstructed displacement accuracy, the modal order would be optimized using particle swarm algorithm (PSO), aiming to minimize the ill conditioned degree of transformation modal matrix and the displacement reconstruction error. Numerical simulation and dynamic load testing results show that the reconstructed displacement was in good agreement with the simulated or measured results, which verifies the validity and accuracy of the algorithm proposed in this paper.