• 한국분무공학회지
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• 제21권3호
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• pp.155-161
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• 2016

Injected fuel pressure waves of a common rail injector with various current profiles supplied to the injecor were measured using Bosch method. In order to drive the common rail injector, the current in the solenoid should be controlled using what is known as a peak and hold pattern, which consists of a high current level with a short time duration (peak) in the first step and a low current level with a long time duration (hold) in the subsequent step. The current profile can be shaped by swithcing an injector driving power source with the peak and hold waves. The capture, compare and PWM (CCP) pin in the microprocessor was used to generate the combined peak and hold waves. The PWM square wave generated from the CCP pin has a duty ratio of 100% for the peak current and 10% or 30% for the hold pattern. Five patterns of the current profile were generated by combining the peak and hold wave. The common rail pressure is controlled at 75, 100, and 130 MPa. As the fuel rail pressure increases, the variations of the measured fuel injection pressure wave according to the current profiles decrease.

• 한국산학기술학회논문지
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• 제14권11호
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• pp.5338-5343
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• 2013

햅틱 시스템에서 가상 벽의 스프링상수 (Kw)가 크면 클수록 사용자는 실제 벽처럼 느끼지만 햅틱 시스템은 그만큼 불안정해진다. 그래서 시스템의 안정성을 유지하면서 가상 벽에 대한 사용자 몰입감을 향상시키기 위해서 일차 홀드 방식을 이용한 방법을 제시하고자 한다. 특히 가상 벽 (virtual wall)로 구성된 가상 환경과 상호 작용할 때 일차홀드 (FOH) 방식을 이용하는 경우 햅틱 장치의 물성치인 질량 (Md)과 댐핑 상수 (Bd)가 시스템의 안정성에 미치는 영향을 분석한다. 시뮬레이션을 통해 시스템의 안정성을 유지하는 가상 벽의 스프링 상수 (Kw)가 햅틱 장치의 질량 (Md)과 댐핑 상수 (Bd)의 제곱근에 비례한다는 것을 보이고, 이를 통해 기존의 영차홀드 (ZOH) 방식보다 큰 가상 스프링의 구현이 가능함을 보인다. 따라서 사용자의 몰입감 높은 햅틱 시스템 구현이 가능함을 보인다. 그리고 시뮬레이션 결과분석을 통해 시스템 안정성을 보장하는 가상 스프링 상수 (Kw)의 범위를 샘플링 주기 (T), 햅틱 장치의 질량 (Md), 댐핑 상수 (Bd)의 관계로 유도한 결과가 $K_w{\leq}{1.611M_d}^{0.50}{B_d}^{0.50}T^{-1.51}$ 임을 보인다. 이 때 시뮬레이션 결과와의 상대 오차가 평균 0.53%로 매우 작다.

• 대한수학회지
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• 제35권2호
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• pp.399-422
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• 1998

A useful method of proving the finite decidability of an equationally definable class V of algebras (i.e., variety) is to prove the decidability of the class of finite directly indecomposable members of V. The validity of this method relies on the well-known result of Feferman-Vaught: if a class K of first-order structures is decidable, then so is the class {$\prod$$_{i}$＜n/ $A_{i}$│ $A_{i}$ $\in$ X (i < n), n $\in$ $\omega$}. In this paper we show that the converse of this does not necessarily hold.d.d.

• 한국대기환경학회지
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• 제17권1호
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• pp.51-56
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• 2001

This study was carried out to interpret mathematically hydraulic behaviour in packing tower which packed 50 mm plastic Hiflow-ring with a dimension of 300 mm wide and 1,400 mm high. In view of energy saving, the recent packing. 50 mm plastic Higlow-ring was superior to conventional packings because of low pressure drop in high loads. As relative error between numerically predicted and experimentally obtained values was less then 6% in the loading and flooding point, it found that therir results appeared to be adequate. Comparison of hose two values in both dry and wet packing conditions. relative errors amount to 3.96 and 5.6%, respectively. In order to evaluate the operating characteristics of packing, the type, size, and material for packings must be estimated in various system and loads. This study is able to calculated pressure drop, hold-up, gas and liquid loads using mathematical interpretation. For these calculation, the specific constants of each packings must be calculated first all. The method of mathematical interpretation in this study turned out to be superior to the existing methods because of reduced errors at loading and flooding point.

• 공학교육연구
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• 제13권2호
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• pp.64-69
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• 2010

Electronics machines make daily human life more convenient and comfortable and try to ease burdens. When designing and manufacturing such mechatronic systems, the engineers need to have a wide range of knowledge. The purpose of our education is for students to learn to use mechatronic techniques. To realize our goal, we regard "an interest in creation" of our student as an important educational method. In this paper, we propose and try an educational method for mechatronics creation using "their interest". The method is to hold robot competitions between 1st and 3rd year students as a regular curriculum. In order to confirm the progress of our students in our engineering course, in the last year, some students entered the Rescue Robot Contest held in Kobe Japan. As a result, our student team got second place, a great honor considering it was our first attempt. We confirm that the robot competition is a useful method to make students study by themselves.

• Structural Engineering and Mechanics
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• 제89권3호
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• pp.265-281
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• 2024

The sound radiation responses of multi-layer composite plates subjected to harmonic mechanical excitation in hygrothermal environment is numerically investigated. A homogenized micromechanical finite element (FE) based on the higher-order mid-plane kinematics replicating quadratic function as well as the through the thickness stretching effect together with the indirect boundary element (IBE) scheme has been first time employed. The isoparametric Lagrangian element (ten degrees of freedom per node) is used for discretization to attain the hygro-thermo-elastic natural frequencies and the modes of the plate via Hamilton's principle. The effective material properties under combined hygrothermal loading are considered via a micromechanical model. An IBE method is then implemented to attain structure-surrounding coupling and the Helmholtz wave equation is solved to compute the sound radiation responses. The effectiveness of the model is tested by converging it with the similar analytical/numerical results as well as the experimentally acquired data. The present scheme is further hold out for solving diverse numerical illustrations. The results revealed the relevance of the current higher-order FE-IBE micromechanical model in realistic estimation of hygro-thermo-acoustic responses. The geometrical parameters, volume fraction of fiber, layup, and support conditions alongside the hygrothermal load is found to have significant influence on the vibroacoustic characteristics.

• Geomechanics and Engineering
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• 제5권1호
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• pp.37-55
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• 2013

An important issue in the design of soil-nailing systems, as long-term retaining walls, is to assess their stability during seismic events. As such, this study is aimed at simulating the dynamic behavior and failure pattern of nailed structures using two series of numerical analyses, namely dynamic time history and pseudo-static. These numerical simulations are performed using the Finite Difference Method (FDM). In order to consider the actual response of a soil-nailed structure, nonlinear soil behaviour, soil-structure interaction effects, bending resistance of structural elements and construction sequences have been considered in the analyses. The obtained results revealed the efficiency of both analysis methods in simulating the seismic failure mechanism. The predicted failure pattern consists of two sliding blocks enclosed by three slip surfaces, whereby the bottom nails act as anchors and the other nails hold a semi-rigid soil mass. Moreover, it was realized that an increase in the length of the lowest nails is the most effective method to improve seismic stability of soil-nailed structures. Therefore, it is recommended to first estimate the nails pattern for static condition with the minimum required static safety factor. Then, the required seismic stability can be obtained through an increase in the length of the lowest nails. Moreover, placement of additional long nails among lowest nails in existing nailed structures can be considered as a simple retrofitting technique in seismic prone areas.

• 한국산학기술학회논문지
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• 제15권4호
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• pp.1813-1818
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• 2014

햅틱 시스템에는 사용자인 인간이 항상 포함되므로, 인간 임피던스에 의한 시스템 안정성 분석이 필요하다. 특히, 일차 홀드 방식의 햅틱 시스템에 대한 인간 임피던스의 안정성 영향 분석이 미진하다. 본 논문에서는 선형 2차 시스템으로 모델화된 인간의 임피던스 모델을 포함하는, 일차 홀드 방식의 햅틱 시스템에 대한 안정성을 루드-후르비쯔 (Routh-Hurwitz)안정성 판별법을 이용하여 해석했다. 가상 벽 모델인 가상 스프링 상수 ($K_w$)의 안정성 영역과 인간 임피던스의 질량 ($M_h$), 댐핑 ($B_h$),그리고 스프링 상수 ($K_h$)와의 관계를 루드-후르비쯔 안정성 판별법을 이용하여 분석한 결과, 스프링 상수 ($K_h$)가 일정할 때 가상 스프링 상수 ($K_w$)는 인간 임피던스의 질량 ($M_h$)과 댐핑 ($B_h$)의 제곱근에 비례했다. 또한 인간 임피던스의 질량 ($M_h$)또는 댐핑 ($B_h$)가 일정할 때 가상 스프링 상수 ($K_w$)는 스프링 상수 ($K_h$)의 0.48배만큼 감소했다. 이를 종합하여 $K_w{\leq}54413{\sqrt{(M_h+M_d)(B_h+B_d)}}-0.486K_h$의 모델을 제안했고, 이론 값들과 제시된 모델로부터 계산된 값을 비교한 결과 평균적인 상대오차가 0.5%로 작게 나타났다. 제시된 모델이 인간 임피던스 모델과 가상 스프링 상수와의 관계를 비교적 잘 표현하고 있다.

• 대한공업교육학회지
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• 제36권1호
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• pp.131-148
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• 2011

이 연구의 목적은 기술 가정교과에서의 녹색성장 교육과 관련된 연구에 기초 자료를 제공하기 위하여 녹색 정보기술 실천방안을 개발하고 녹색 정보기술 실천방안을 적용한 수업이 학생의 녹색 정보기술 실천에 영향을 미치는지를 구명하는데 있다. 이 연구의 목적을 달성하기 위해 첫째, 문헌 분석을 통해 녹색 정보기술 교육의 실천방안을 개발하였고, 녹색 정보기술 실천 방안을 적용한 검사지를 제작하였다. 둘째, 녹색 정보기술 실천 방안을 수업에 적용하였다. 셋째, 녹색 정보기술 실천 방안 검사지를 통해 대전에 위치한 D중학교 학생(남 62명, 여 59명)을 대상으로 사전 사후검사를 실시하여 결과를 비교하였다. 연구를 통해 도출한 결론은 다음과 같다. 첫째, 녹색 정보기술 실천방안 적용 수업이 컴퓨터, 모니터 및 데이터 둥 학생들이 생활 속에서 직접적으로 접하는 항목의 녹색 정보기술 실천에 긍정적인 영향을 미쳤다. 이러한 점을 통해 향후 기술 가정 교과에서 녹색성장 교육과정 개발 시 생활과 밀접한 내용을 보다 많이 고려하여 편성하여야 함을 알 수 있었다. 둘째, 녹색 정보기술 실천 방안 적용 수업이 프린터, 주변기기 및 기타 항목에서의 녹색 정보기술 실천에는 별다른 영향을 미치지 못하였다. 그러나 향후 보다 많은 학생들이 프린터 및 주변기기를 보유할 것을 예상하여 이러한 항목들에 대한 실천 방안을 보다 면밀히 연구할 필요가 있음을 알 수 있었다. 셋째, 녹색 정보기술 실천에 대한 남학생과 여학생의 차이는 없었다. 이를 통해 녹색성장과 관련된 교육 내용을 편성할 때 남학생과 여학생을 특별히 구분하여 개발할 필요가 없음을 알 수 있었다.

• 무역상무연구
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• 제77권
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• pp.259-284
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• 2018

The purpose of this study is to identify the determinants of the export performance of the most preferred trade exhibitions for SMEs. And the results are as follow. First, it is analyzed that the challenging entrepreneurship, the global orientation toward the overseas market, the quality of the excellent trade show, and the support system of the trade exhibition of the export related organizations all have a very positive effect on the export performance of the SMEs participating in the trade show. Second, the number and size of participating trade shows has no influence on controlling export performance. Third, there is a difference in export performance depending on participation frequency, participation size, participation method, and participating region. The implication of this study is that SMEs, which have a strong sense of entrepreneurship and a strong commitment to the global market, need to actively participate in trade exhibitions with relatively low barriers to entry. The policy implication is that organizers and export-related organizations need to understand the internal capabilities of participating companies in order to maximize the performance of participating companies. And Korea should also create an environment that can attract and hold excellent trade exhibitions held overseas. Therefore, the government and export-related organizations should expand the infrastructure for hosting global trade exhibitions. As well as an urgent need to build a system for attracting overseas buyers that can dramatically boost overseas buyer visits.