• Proceedings of the Korean Society of Precision Engineering Conference
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• 1993.10a
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• pp.660-665
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• 1993

An elastic model is developed to predict the average thermal residual stresses in the matrix and fiber of a misoriented short fiber composite. The thermal residual stresses are induced by the mismatch in the coefficient of the thermal expansion of the matrix and fiber when the composite is subjected to a uniform temperature change. The model considers two special cases of fiber misorientation ; two-dimensional in-plane and three-dimensional axisymmetric. The analytical formulation of the model is based on Eshelby's equivalent inclusion method and is nuque in that it is able to account for interactions among fibers. The model is more general than past models and it is able to treat prior analyses of the simpler composite systems as extram cases. The present model is to investigate the effects of fiber volume fraction, distribution type, distribution cut-off angle, and aspect ratio on thermal residual stress for both in-plane and axisymmetric fiber misorientation. Fiber volum fraction, aspect ratio, and disturbution cut-off angle are shown to have more significant effects on the magnitude of the thermal residual stress than fiber distrubution type for both in-plane and axisymmetric misorientation.

• The Journal of Korea Robotics Society
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• v.5 no.1
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• pp.70-76
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• 2010

This paper addresses a design issue of "model complexity and performance trade-off" in the application of bandwidth extension (BWE) methods to the intra-frame predictivevector quantization problem of wideband speech. It discusses model-based linear and non-linear prediction methods and presents a comparative study of them in terms of prediction gain. Through experimentation, the general trend of saturation in performance (with the increase in model complexity) is observed. However, specifically, it is also observed that there is no significant difference between HMM and GMM-based BWE functions.

• The Journal of Korea Robotics Society
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• v.4 no.4
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• pp.273-280
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• 2009

It is difficult to find a practical solution for the backward-motion control of a car-like mobile robot with n passive trailers. Unlike an omni-directional robot, a car-like mobile robot has nonholonomic constraints and limitations of the steering angle. For these reasons, the backward motion control problem of a car-like mobile robot with $n$ passive trailers is not trivial. In spite of difficulties, backing up a trailer system is useful for parking control. In this study, we proposed a mechanical alteration which is connecting $n$ passive trailers to the front bumper of a car to improve the backward motion control performance. Theoretical verification and simulations show that the backward-motion control of a general car with n passive trailers can be successfully carried out by using the proposed approach.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.2
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• pp.155-164
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• 1998

A multi-type heat pump controls the mass flow rate of the working fluid to cope with variable heat loads when it is under dynamic load condition. This paper describes the exergy analysis associated with the dynamic response of heat pump. First, a basic heat pump cycle is examined at steady state to show the general trends of exergy changes in each process of the cycle. Entropy generation issue in the exchangers is discussed to optimize the heat pump cycle. Second, the performance of the inverter-driven heat pump is compared to that of the conventional one when the heat load is variable. Third, the exergy destruction rate associated with the ON/OFF operations of the heat pump is calculated by simulating the thermodynamic states of the condenser and the evaporator. The inefficiency of the ON/OFF operation during the transient period is quantitatively revealed by the exergy analysis.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.537-542
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• 1999

The design methodologies for carbon fiber sheet(CFS) strengthening of RC structures are not well established yet because the structural behavior of strengthened RC structures is more complex than that of unstrengthened ones. Even though the research for the methods using CFS has beed studied, the strengthening effects and structural behaviors of strengthened structures are not systematized yet. The purpose of this study is to carry out the experimental studies on three kinds of half scale RC slab bridges and to investigate the behavior of RC slab bridges from the experimental results. Typical flexural failure occurs in the non-strengthening slab like general RC slab bridges, and also the flexural failure occurs in the all area strengthened slab with sudden rip-off failure of strengthening material by punching shear. For the case of strip type strengthened slab, flexural failure occurs, with rip-off of second strip at the base of loading point. Strengthening effect on the slab using CFS is that the strength is increased upto 7~15 percent and the crack pattern is changed.

• Proceedings of the IEEK Conference
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• 2008.06a
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• pp.1103-1104
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• 2008

In this paper, authors propose a novel step-up AC-DC chopper operated with power factor correction (PFC) and with high efficiency. The proposed chopper behaves with discontinuous current control (DCC) of input current. The input current waveform in the proposed chopper is got to be a discontinuous sinusoid form in proportion to magnitude of ac input voltage under the constant duty cycle switching. Therefore, the input power factor is nearly unity and the control method is simple. In the general DCC chopper, the switching devices are turned-on with the zero current switching, but turn-off of the switching devices is switched at current maximum value. To achieve a soft switching of the switching turn-off, the proposed chopper is used a new partial resonant circuit. The result is that the switching loss is very low and the efficiency of chopper is high.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.37-42
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• 1997

Off-line feed rate scheduling is an advanced methodology to automatically determine optimum feed rates for the optimization of NC code. However, the present feed rate scheduling systems have lim~tations to generate the optimized NC codes because they use the material removal rate or non-generalized cutting force model. In this paper, a feed rate scheduling system based on an improved cutting force model that can predrct cutting forces exactly in general machining was presented. Original blocks of NC code were divided to small ones with the modified feed rates to adjust the peak value of cutting forces to a constant vale. The characteristic of acceleration and deceleration for a given machrne tool was considered when off-line feed rate scheduhng was performed. Software for the NC code optimization was developed and applied to pocket machining simulation.

• The Korean Journal of Applied Statistics
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• v.17 no.3
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• pp.393-402
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• 2004

We suggest a summary of sample design for the statistical survey of E-commerce to estimate the general trend as well as the market size and investment scale of e-commerce based on the Census on Basic Characteristic of Establishments(CBCE). The sample design of this survey is composed of systematic sampling and modified cut-off method.

• 한국해양학회지
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• v.28 no.2
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• pp.121-131
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• 1993

The tidal front forming in the Mid-Yellow Sea off Korea, near Tae-An peninsular, is calculated using a 3-D general circulation model(Semtner, 1974) and the concept of mixing rate, an extension of the concept of mixing efficiency proposed by simpson & Hunter(1974). Along the north and south open boundaries, simple radiation conditions are applied. The model is run with the initial state which represents the winter condition. With imposed uniform heating by solar radiation and spatially-different vertical mixing, the model then generated the tidal front comparable to the observed one.

• Korean Journal of Computational Design and Engineering
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• v.7 no.1
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• pp.18-26
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• 2002

The suggested modular projection system can have flexible arrangements of screens. Modular and continuous arrangements of the display system enable us to modify the screen configuration easily, so that the system can be used in various applications. The image of each screen is calculated automatically by using window projection and the tracked position of the viewer. This system also uses the off-axis stereoscopic projection for the seamless stereoscopic edge blending of multiple connections of screens. The system has been successfully tested for the general navigation model and the CAU driving simulator with motion platform.