• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.348-352
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• 2002

a basis such as IT(Information Technology), NT(Nano Technology) and BT(Bio Technology). Recently, NT is applied to various fields that are composed of science, industry, media and semiconductor-micro technology. It has need of IT that is ultra-precision positioning technology with strokes of many hundreds mm and maintenance of nm precision in fields of ultra micro process, ultra precision measurement, photo communication part and photo magnetic memory. This thesis represents optimal design on ultra-precision positioning with single plane X-Y stage and development of artificial control system for adequacy of industrial demand. Also, dynamic simulation on global stage is performed by using ADAMS (Automated Dynamic Analysis of Mechanical System) for the purpose of grasping dynamic characteristic on user designed X-Y global stage. The error between displacements from micro stage and from FEM(Finite Element Method) is 3.53% by verifications of stability on micro stage and control performance. As maximum Von-mises stress on hinge of micro stage is 5.981kg/mm$^2$ that is 1.5% of yield stress, stability on hinge is secured. Preparing previous results, optimal design of micro stage can be possible, and reliance of results with FEM can be secured.

• International Journal of Highway Engineering
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• v.14 no.5
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• pp.57-65
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• 2012

PURPOSES: It is important to consider the long-term performance of concrete pavement, because concrete pavement is more exposed to the various environmental conditions than any other concrete structures. One of the several methods to evaluate the long-term performance of concrete during winter is KS F 2456. Relative dynamic modulus of elasticity shows the resistance to freezing and thawing. METHODS: To measure relative dynamic modulus of elasticity, ultra sonic is generally used. But in this study, to measure the relative dynamic modulus of elasticity, both ultra sonic and shear wave were used and then compared each other. RESULTS: The results from the measurement by ultrasonic wave and shear wave were divided into three types. Type 1 : Specimens are good and relative dynamic modulus of elasticity did not decrease until 300 cycle. Type 2 : The relative dynamic modulus of elasticity decreased from the late cycle.(about 150 cycle later) Type 3 : The relative dynamic modulus of elasticity consistently decreased from the beginning. As a result of ANOVA, there is no difference according to measuring method, in type 2 and 3. But there is a difference according to measuring method, in type 1's relative dynamic modulus of elasticity. CONCLUSIONS: It is proved that shear wave can be used to understand the damage tendency of relative freezing and thawing and to measure the relative dynamic modulus of elasticity.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.4 s.235
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• pp.624-631
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• 2005

A note-book PC has become thinner in recent years, which requires the optical disc drives with small height and high memory capacity. Therefore the actuator of optical disc drives must be thinner and have disc tilt compensation function for high density memory. In this paper, the actuator with hybrid type is investigated for 3-axis ultra-slim actuator. A 3-axis ultra-slim actuator is designed by using the modal analysis of the actuator and the electromagnetic analysis of magnetic circuit to achieve dynamic characteristics. Also, magnetic force between tilt magnet and tilt yoke is investigated to and the influence on the DC sensitivity in the focus and track directions.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.306-309
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• 2009

The influence of equal-channel angular pressing (ECAP) route on dynamic deformation behavior of ultra-fine grained Al-4.4%Mg alloys was investigated in this study. The 8-pass ECAPed specimens consisted of ultra-fine grains of $0.5{\mu}m$ in size, and contained the considerable amount of second phase particles, which were fragmented and distributed homogeneously in the matrix. The result of dynamic torsional tests indicated that the maximum shear stress and fracture shear strain were lowest in the specimen deformed by ECAP via route A among the 8-pass ECAPed specimens. The formation of adiabatic shear bands was addressed by concepts of critical shear strain, deformation energy required for void initiation, and microstructural homogeneity related to ECAP routes.

• Macromolecular Research
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• v.12 no.1
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• pp.141-143
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• 2004

We have investigated the dynamic mechanical behavior of ultra-high molecular weight polyethylene (UHMWPE) irradiated with varying doses of gamma rays. A relaxation peak in the loss factor curve, which has not been reported previously in the literature, is observed at a temperature above the crystal melting temperature. The peak is unique to UHMWPE and appears to be related to the high degree of entanglement. Because the temperature and intensity of the peak are reduced by irradiation-induced chain scission and crosslinking, respectively, we believe that the peak is associated with disentanglement relaxation. The behavior of the storage modulus in the melt state agrees with the classical theory of rubber elasticity.

• Journal of Electrical Engineering and Technology
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• v.13 no.1
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• pp.97-104
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• 2018

This paper proposes supplementary control of conventional coordinated control of a power plant which directly affects network frequency. The supplementary control with dynamic matrix control is applied for 1000 MW power plant with ultra-supercritical (USC) once-through boiler. The supplementary control signal is added to the boiler feedforward signal in the existing coordinated control logic. Therefore, it is a very practical structure that can maintain the existing multi-loop control system. This supplementary controller uses the step response model for the power plant system, and on-line optimization is performed at every sampling step. The simulation results demonstrate the effectiveness of the proposed supplementary control in a wide operating range of a practical 1000 MW USC power plant simulator. These results can contribute the stable operation of power system frequency.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.208-213
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• 2003

A note-book PC has become thinner in recent years. And optical disc drives are required to have high memory capacity. Therefore, the actuator of optical disc drives must be thinner and have disc tilt compensation function for high density memory. In this paper, the hybrid type actuator is investigated for 3-axis ultra-slim actuator. A 3-axis ultra-slim actuator is designed by using the modal analysis of the actuator and the electromagnetic analysis of magnetic circuit to achieve dynamic characteristics and magnetic flux density for high sensitivity, respectively. Also, magnetic force between tilt magnet and tilt yoke is investigated to find the influence on the DC sensitivity in the focus and track directions.

• Transactions of Materials Processing
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• v.30 no.5
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• pp.247-254
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• 2021

This study reviews dynamic deformation behavior of ultra-fine-grained Al alloys, ultra-fine-grained conventional low carbon steel and dual phase steel and Zr-based amorphous alloys. Dynamic tests were conducted using a Kolsky bar then the test data was analyzed in relation to resultant microstructures, mechanical properties and propensity of adiabatic shear band. In addition, deformed microstructures and fracture surfaces were used to investigate the behavior of both the dynamic deformation and fracture, and adiabatic shear banding. As a result, increasing microstructural homogeneity, strain hardenability and forming multiple shear bands could be a better way to increase the fracture resistance under dynamic loading as the formation of adiabatic shear bands was reduced or prevented.

• Structural Engineering and Mechanics
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• v.73 no.4
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• pp.427-436
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• 2020

The use of final IGS precise orbit and clock products for high-rate GNSS-PPP proved its effectiveness in capturing dynamic displacement of engineering structures caused by earthquakes. However, the main drawback of using the final products is that they are available after approximately two weeks of data collection, which is not suitable for timely measures after an event. In this study, the use of ultra-rapid products (observed part), which are available after a few hours of data collection, and rapid products, which are available in less than 24 hrs, are investigated and their results are compared to the more precise final products. The tests are designed such that harmonic oscillations with different frequencies and amplitudes and ground motion of a simulated real earthquake are generated using a single axis shake table and the PPP was used to capture these movements by monitoring time-change of the table positions. To evaluate the accuracy of PPP using ultra-rapid, rapid and final products, their results were compared with relative GNSS positioning and LVDT (Linear Variable Differential Transformer) data, treated as reference. The results show that the high-rate GNSS-PPP solutions based on the three products can capture frequencies of harmonic oscillations and dynamic displacement with good accuracy. There were slight differences between ultra-rapid, rapid and final products, where some of the tested events indicated that the latter two produced are more accurate and provide better results compared to the ultra-rapid product for monitoring short-term dynamic displacements.

• Journal of the Korean Society for Railway
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• v.18 no.2
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• pp.117-126
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• 2015

The development of railway roadbed for 600km/h train speed level is very difficult because unpredictable static and dynamic interaction occurs between the ultra-high speed train and the infrastructure. Especially, an earthwork-bridge transition zone is a section in which influential factors react, such as bearing capacity, compression, settlement, drainage, and track irregularity; these interactions can include complicated dynamic interaction. Therefore, if static and dynamic stability are secured in transition zones, it is possible to develop roadbeds for ultra-high speed railways. In the present paper, design parameters for transition reinforcement applied to present railway design criteria are analytically examined for ultra-high speed usage on a preferential basis. Design parameters are the presence of reinforcing materials, geometric shape, stiffness of materials, and so on. Analysis is focused on the deformation response of the track and running stability at ultra-high speed.