• 한국수소및신에너지학회논문집
• /
• 제24권5호
• /
• pp.461-466
• /
• 2013

In this research, the diesel cycle was thermodynamically interpreted to evaluate the possibility of high efficiency by converting diesel engine to the atkinson cycle, and general cycle features were analyzed after comparing these two cycles. That an experimental single cylinder and a long stroke diesel-atkinson engine, of which S/B ratio was more than 3, were manufactured. After evaluating the engine through basic experiments, a diesel engine was converted into the atkinson cycle by constituent VCR (variable compression ratio) device and VVT (variable valve timing) system. The experimental method was to observe compression work reduction effects due to low compression effects from delayed intake valve closing of the early stage atkinson engine. The result, the possibility of increasing compression ratio about each engine load was confirmation by constructing compensate expansion-compression ratio in accordance with the delayed intake valve close.

• 대한기계학회논문집
• /
• 제13권2호
• /
• pp.213-220
• /
• 1989

본 연구에서는 고정도의 위치제어계를 실현하기 위하여 가변구조제어이론을 전기-유압서보계에 적용하였다.실험은 유압구동부의 공급압력을 변화시켜 유압계의 매개변수를 변화시켜줄 때와 관성하중을 가감하여 부하를 변화시켜 가며 행하였다. 가변구조계에서는 계의 매개변수변동과 부하변동에도 영향을 받지 않음을 종래의 고정구조계와 구조계와 비교, 검토하였다.

• 한국학교수학회논문집
• /
• 제4권1호
• /
• pp.103-114
• /
• 2001

The purpose of this study is to develop learning materials for functional concept on variable and to verify the effect of how well students could learn functional concept after they studied with those materials. To accomplish the purpose of this study, I developed learning materials and after teaching students with them. I have concluded the followings : First, there was little effect in teaching functional concept on variable between two experimental groups, whereas teaching functional concept had greater effect on forming functional concept in high level groups in those two experimental groups. Second, teaching functional concept on variable had little effect on students' understanding of functional concept and perfecting tables in Black box, graph, and mathematical problems, whereas there was much effect in students' understanding functional concept and solving relation formula, image, and range problems related to everyday life or general things. On the basis of the problems which appeared in the process of this study, the following can be suggested : First, we should develop learning materials fit for low level students so that they could understand functional concept. Second, we should continue to teach the basic problems like solving relation formula, image, and range, and understanding functional concept in graph until students are able to understand them exactly. Third, since the goals of Unit Function in a middle school textbook is to solve problems related to everyday life through functional thinking, there should be change in constructing systematic contents of Unit Function in a middle school textbook.

• 제어로봇시스템학회논문지
• /
• 제15권5호
• /
• pp.525-529
• /
• 2009

Most of FLC received input data from error e and change-of-error e' with no relation with system complexity. Basic scheme follows typical PD and PI or PID Controller and that has been developed through fixed ME In this paper, We studied the relationship between MF and system response and system response through changing Fuzzy variable of consequence MF and propose the simple FLC using this relationship. The response of FLC is changed according to the width of Fuzzy variable of consequence MF. As changing the Fuzzy variable of consequence MF shows various nonlinear characteristic, we studied the relation between response and MF using analytical method. We designed the effective FLC using three-variable MF and nine rules and took simulation for verification. In this study, we propose the method to design system with FLC in stability point which is an impotent characteristic of designing system. The circle criterion which is adapted to analysis the nonlinear system is put to use for proposed method. Since SISO FLC has a time-invariant and odd characteristic we can use the critical point not disk which is generally used to determine the stability in the circle criterion, to determine the stability. Using this, we can get the maximum critical point plot of SISO FLC with changing the consequence fuzzy variables. The predetermined critical point plot of FLC can be used to decide the region of the system to be stable. This method is effectively used to design the SISO FLC.

• International journal of advanced smart convergence
• /
• 제10권4호
• /
• pp.256-262
• /
• 2021

In order for small electric vehicles to drive on hilly roads in Korea, methods to improve the climbing ability and power performance of vehicles should be taken. In order to improve the power performance of small electric vehicles, the performance of motors mounted on electric vehicles should be improved. However, if the performance of the motor is improved to improve the power performance of the electric vehicle, it is possible to lower the price competitiveness accordingly. In addition, the power consumption of the battery is rapidly increased to drive the high-performance motor, so in order to introduce the small electric vehicle into the domestic market, various problems must be overcome. In order to commercialize small electric vehicles that do not emit harmful exhaust gases to the human body in the hilly domestic terrain, it is effective to introduce a separate continuously variable transmission system that can improve the climbing ability and power transmission ability. In this study, we propose a proprietary model of continuously variable transmissions that can be applied to small electric vehicles. The proposed continuously variable transmission is equipped with a spring in the driving pulley and the driven pulley, and has the advantage of performing a shift that increases torque in a situation where the vehicle needs to increase torque when driving on a hill. In addition, the basic design for commercialization of the proposed continuously variable transmission was carried out, and the prototype manufactured and attached to the body of a small electric vehicle.

• 분석과 대안
• /
• 제7권3호
• /
• pp.1-26
• /
• 2023

This article will analyze and forecast important variables and dynamics in global power politics after the war in Ukraine. It tries to use several perspectives to analyze international relations, particularly liberal internationalism and structural realism. In short, core variables are as follows; First, how is the US-led liberal international order and globalization being adjusted? Second, how will the U.S.-China strategic competition, which is the biggest and structural variable, cause changes in the international order in the future? The third variable, how stable are Sino-Russia relations in the context of a structuring U.S.-China-Russia strategic new triangle? Fourth, to what extent will third middle hedging states outside the U.S. and China be able to exercise strategic autonomy in the face of multipolarization? To summarize, the first of these four variables is the largest basic variable at the global political and economic level in terms of its impact on the international community, and it has been led by the United States. The second variable, in terms of actors, seems to be the most influential structural variable in global competition, and the US-China strategic competition is likely to be a long game. Thus the world will not be able to escape the influence of the competition between the two global powers. For South Korea, this second variable is probably the biggest external variable and dilemma. The third variable, the stability of Sino-Russia relations, determines balance of global power in the 21st century. The U.S.-China-Russia strategic new triangle, as seen in the current war in Ukraine, will operate as the greatest power variable in not only global power competition but also changes in the international order. Just as the U.S. is eager for a Sino-Russia fragmentation strategy, such as a Tito-style wedge policy to manage balance of power in the early years of the Cold War, it needs a reverse Kissinger strategy to reset the U.S.-Russia relationship, in order to push for a Sino-Russia splitting in the 21st century. But with the war in Ukraine, it seems that this fragmentation strategy has already been broken. In the context of Northeast Asia, whether or not the stability of Sino-Russia relations depends not only on the United States, but also on the Korean Peninsula. Finally, the fourth variable is a dependent variable that emerged as a result of the interaction of the above three variables, but simultaneously it remains to be seen that this variable is likely to act as the most dynamic and independent variable that can promote multilateralism, multipolarization, and pan-regionalism of the global international community in the future. Taking into account these four variables together, we can make an outlook on the change in the international order.

• 한국수소및신에너지학회논문집
• /
• 제17권3호
• /
• pp.255-262
• /
• 2006

To develop a hydrogen fueled engine with external mixture which uses in high reliability, low cost and low pressure, the single cylinder research engine with MCVVT(Mechanical Continuous Variable Valve Timing) system is developed and its basic characteristics analyzed. The MCVVT developed has high reliability and the valve timing change is possible in wide range continuously. Though the mechanical loss due to MCVVT system is increased a little, back-fire suppression research for valve overlap period is no difficulty. It's also confirmed that the hydrogen-fueled engine has lower torque and is possible high lean burn. As fuel-air equivalence ratio is high, as thermal efficiency is remarkable increasing.

• Journal of Information Technology Applications and Management
• /
• 제17권3호
• /
• pp.163-189
• /
• 2010

The purpose of this research is to develop a decision-making model for the calculation of the National Disaster Management System's standard prevention workforce quota. The final purpose of such model is to support in arranging a rationally sized prevention workforce for local authorities by providing information about its calculation in order to support an effective and efficient disaster management administration. In other words, it is to establish and develop a model that calculates the standard disaster prevention workforce quota for basic local governments in order to arrange realistically required prevention workforce. In calculating Korea's prevention workforce, it was found that the prevention investment expenses, number of prevention facilities, frequency of flood damage, number of disaster victims, prevention density, and national disaster recovery costs have positive influence on the dependent variable when the standard prevention workforce was set as the dependent variable. The model based on the regression analysis-which consists of dependent and independent variables-was classified into inland mountainous region, East coast region, Southwest coastal plain region to reflect regional characteristics for the calculation of the prevention workforce. We anticipate that the decision-making model for the standard prevention workforce quota will aid in arranging an objective and essential prevention workforce for Korea's basic local authorities.

• 설비공학논문집
• /
• 제26권1호
• /
• pp.32-37
• /
• 2014

The thermal contact resistance (TCR) is one of the important resistance components in cryogenic systems. Cryogenic measurement devices using a cryocooler can be affected by TCR because the device has to consist of several metal components that are in contact with each other for heat transfer to the specimen without a cryogen. Therefore, accurate measurement and understanding of TCR is necessary for the design of cryogenic measurement devices using a cryocooler. The TCR occurs at the interface between metals and it can be affected by variable factors, such as the roughness of the metal surface, the contact area and the contact pressure. In this study, we designed a TCR measurement system at variable temperature using a cryocooler as a heat sink. Copper was selected as a specimen in the experiment because it is widely used as a heat transfer medium in cryogenic measurement devices. We measured the TCR between Cu and Cu for various temperatures and contact pressures. The effect of the interfacial materials on the TCR was also investigated.

• 전자공학회논문지SC
• /
• 제46권3호
• /
• pp.31-35
• /
• 2009

본 논문에서는 무선통신에서 데이터 변환을 위하여 2개의 계수 값에 의하여 중간 주파수를 조절할 수 있는 개선된 구조를 가지는 4차 SC Bandpass ${\sigma}-{\Delta}$ 모듈레이터 구조를 제안한다. 제안한 구조는 4차 형태의 잡음 전달함수를 원하는 형태로 변경할 수 있고, 또한 기존구조는 중간주파수 조절을 위한 다른 8개의 클록과 가변이 가능한 4개의 계수 값이 필요하지만 제안한 구조는 가변이 가능한 2개의 계수 값과 기본 클록만으로 중간주파수를 조절할 수 있다.