• Tribology and Lubricants
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• v.37 no.2
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• pp.77-80
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• 2021

In this study, we investigated the effect of the spring constant on frictional behavior at a nanoscale through molecular dynamics simulation. A small cube-shaped tip was modeled and placed on a flat substrate. We did not apply the normal force to the tip but applied adhesive force between the tip and the substrate. The tip was horizontally pulled by a virtual spring to generate relative motion against the substrate. The controlled spring constant of the virtual spring ranged from 0.3 to 70 N/m to reveal its effect on frictional behavior. During the sliding simulation, we monitored the frictional force and the position of the tip. As the spring constant decreased from 70 to 0.3 N/m, the frictional force increased from 0.1 to 0.25 nN. A logarithmic relationship between the frictional force and spring constant was established. The stick-slip instability and potential energy slope increased with a decreasing spring constant. Based on the results, an increase in the spring constant reduces the probability of trapping in the local minima on the potential energy surface. Thus, the energy loss of escaping the potential well is minimized as the spring constant increases.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.5
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• pp.97-102
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• 2018

Combat vehicles require high levels of maneuverability, firepower, armor, and operability. A high-performance power system is required for optimal maneuverability. The fuel pump which supplies fuel stably is very important to achieve this. The fuel pump consists of a pump part, a motor part, and a control part. It is equipped with a BLDC motor. Numerous failures of the fuel pump occurred during vehicle operation when exposed to vibration, shock, and high temperature. The cause of failure was confirmed to be stator slip of the BLDC motor. Stator slip is a consequence of the interference loss between the stator and the housing of the motor part in an high temperature environment. The failure of the fuel pump was solved through size control of the motor housing and the stator. We performed vibration testing at high temperature for verification. This study contributes to improving the reliability of combat vehicles.

• Korean Journal of Soil Science and Fertilizer
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• v.47 no.6
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• pp.425-431
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• 2014

Most fields in highland areas are covered with rye or hairy vetch for conservation during a fallow. However, using cover crops needs an effort to sow, and this makes top soil more vulnerable to loss due to surface disturbances. The aims of this study were to develop an automatic seeding-regulator device using a low-price, extensive-use GPS sensors and a DC motors and to evaluate a working efficiency of it after adaptation to partial tillage machine for reducing seeding effort. The amount of runoff water and soil loss was evaluated with partial tillage and simultaneous-seeding after harvesting soybean, in 17% slope lysimeters. In results, the seeding amount with the machine speed was stable between $0.5{\sim}0.8m\;s^{-1}$ of working sections. The automatic control device of seeding-rate could be enough to solve the slip problems of power selecting supply system or five four-wheel drive device. In partial tillage and simultaneous seeding, runoff water was 11.6% ($1.8m^3ha^{-1}$) of the scatter-seeding control ($15.5m^3ha^{-1}$) and soil loss was 13.2% ($7kg\;ha^{-1}$) of the scatter-seeding control ($53kg\;ha^{-1}$). These results suggest that partial tillage and simultaneous-seeding methods are very effective in decreasing work effort and soil loss of sloped land.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.10
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• pp.499-504
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• 2017

A Mobile Radio Wave Measurement System (MRWMS)is a vehicle-mounted system designed to be operating in a single mission. The mission characteristic for mobile measurement requires mobility. For this, we must consider the arrangement and embedded method of MRWMS's antennas. In this paper, we described the measurement method design of direction detecting accuracy for MRWMS and designed the direction finding antenna mast capable of rotating itself by using a slip ring without turntable for Direction Finding (DF) accuracy test. As we removed the dependency of a limited local area by designing a measurement method of direction detecting accuracy, Equipment Under Test (EUT) zero-Adjustment and mounted process shortened. So, we the reduced production costs. We expect an improved cable loss value by shortening the RF cable length in accordance with our design. In addition, due to the same phenomenon, the entire system is lighter and the mobility is improved.

• Proceedings of the KIEE Conference
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• 1994.07a
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• pp.579-581
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• 1994

The efficiency optimized speed control system of Induction Motor is proposed At light load, the IM has poor efficiency because of relatively high magnetizing current. In this paper, by employing the field oriented control with flux controller which the motor is operated at optimal slip frequency, the proposed system has good performance and high efficiency. In simulation, the performance, loss and efficiency of the proposed optimal flux control system are compared with those of the coventional constant flux operation. In conclusion, the efficiency is raised by 2.55%, the loss is decreased by 0.1[p.u].

• Journal of the Korea Society for Simulation
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• v.6 no.2
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• pp.1-14
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• 1997

The characteristics of the flow and energy conversion in OMACON liquid-metal MHD system are investigated. Numerical simulation of two-phase flow in the OMACON system without magnetic field was carried out by the Phoenics code and the energy conversion characteristics are studied in association with the fact that the mechanical energy loss at the nozzle of the OMACON system are to be converted into electrical energy. In this system, working fluid (gas) is injected through the mixer located at the bottom of the riser, and is mixed with hot liquid metal. Therefore in the riser two-phase flow is developed under the influence of the gravity. In this study, the interaction between the gas and liquid is considered by the use of IPSA(InterPhase Slip Algorithm) where standard drag coefficient has been used. It has been assumed that in the flow regime the liquid is continuous and the gas is dispersed. For the liquid and gas, the continuity equations, momentum equations and energy equations are solved respectively in association with void fraction in the flow field. In order to calculate the energy conversion efficiency, firstly the ratio of the mechanical energy loss of liquid metal flow at the nozzle to the input thermal energy is considered. Secondly flow pattern of liquid metal in the generator has been analyzed, and the characteristics of the conversion of the mechanical energy into the electrical energy has been investigated. For an representative case where Hartmann number is 540 and magnetic field is 0.35 T, the present analysis shows that the energy conversion efficiency is 0.653. This result is considered to be reasonable in comparison with published experimental results.

• Smart Structures and Systems
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• v.19 no.1
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• pp.57-66
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• 2017

Nanocomposites reinforced with carbon nanotube fibers exhibit greater stiffness, strength and damping properties in comparison to conventional composites reinforced with carbon/glass fibers. Consequently, most of the nanocomposite research is focused in understanding the dynamic characteristics, which are highly useful in applications such as vibration control and energy harvesting. It has been observed that those nanocomposites show better stiffness when the geometry of nanotubes is straight as compared to curvilinear although nanotube agglomeration may exist. In this work the damping behavior of the nanocomposite is characterized in terms of loss factor under the presence of nanotube agglomerations. A micro stick-slip damping model is used to compute the damping properties of the nanocomposites with multiwall carbon nanotubes. The present formulation considers the slippage between the interface of the matrix and the nanotubes as well as the slippage between the interlayers in the nanotubes. The nanotube agglomerations model is also presented. Results are computed based on the loss factor expressed in terms of strain amplitude and nanotube agglomerations. The results show that although-among the various factors such as the material properties (moduli of nanotubes and polymer matrix) and the geometric properties (number of nanotubes, volume fraction of nanotubes, and critical interfacial shear stresses), the agglomeration of nanotubes significantly influences the damping properties of the nanocomposites. Therefore the full potential of nanocomposites to be used for damping applications needs to be analyzed under the influence of nanotube agglomerations.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.4
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• pp.117-122
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• 2006

Maximum efficiency control scheme in a stator flux-oriented induction motor drive is proposed for minimizing input dc power. Flux level is decreased in steps for searching the minimum input dc power. In addition, Torque equation, slip angular frequency, and decoupling compensation current considering iron loss resistance is used. Simulation and experimental results verify the effectiveness of the proposed method.

• Proceedings of the KIEE Conference
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• 1996.07a
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• pp.47-49
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• 1996

The equivalent circuit of LIM is generally composed as the same that of rotary induction motor. However it is very difficult to move the LIM at synchronous velocity for open-secondary circuit test. The resistance representing the core losses in the primary core can not be ignored because the air-gap of LIM is larger than that of rotary induction motor. In this paper, the T-type equivalent circuit of a LIM with the core loss resistance is chosen using static zero slip test and theoritical analysis.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.11
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• pp.2850-2861
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• 1996

This paper describes the design of AATM switch LIS of shared buffer type with linked-list architecture to control memory access. The proposed switch LSI consists of the buffer memory, controller and FIFO memory blocks and two special circuits to avoid the cell blocking. One of the special circuit is a new address control scheme with linked-list architecture which maintains the address of buffer memory serially ordered from write address to read address. All of the address is linked as chain is operated like a FIFO. The other is slip-flag register it will be hold the address chain when readaddress missed the reading of data. The circuits control the buffer memory efficiently and reduce the cell loss rate. As a result the designed chip operates at 33ns and occupied on 2.7*2.8mm$^{2}$ using 0.8.mu.m CMOS technology.