• Journal of Korean Institute of Industrial Engineers
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• v.33 no.2
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• pp.282-289
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• 2007

While demands for express couriers service are rapidly increasing due to recent progress of electronic commerce, express courier service companies are struggling to take a larger market share through ongoing improvement in their service processes. Cut-off time is the time limit that all orders delivered before the limit are guaranteed for the delivery within the very next day. Extending cut-off time for express service centers can provide the express company with increase of total sales, but it may also cause increasing the possibility not to satisfy customer needs due to work delay in the consolidation terminal. We develop a design model for express courier service network based on a recursive optimization/simulation procedure. With the optimization model, we seek key design parameters such as the cut-off time for express service centers and the capacity of the consolidation terminal maximizing total sales profit while satisfying the desired level of performances. With the simulation model, we consider the dynamic nature of the network and obtain relationships between the design parameters and the performance measures with the multiple linear regression. The validity of the model is examined with an example.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.333-336
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• 2003

For long time, the takeoff and landing control of airship was worked by human handling. With the development of the autonomous control system, the exact controls during the takeoff and landing were required and lots of methods and algorithms were suggested. This paper presents the result of airship take-off and landing by buoyancy control using air ballonet volume change and performance control of pitch angle for stable flight within the desired altitude. For the complexity of airship's dynamics, firstly, simple PID controller was applied. Due to the various atmospheric conditions, this controller didn’t give satisfactory results. Therefore, new control method was designed to reduce rapidly the error between designed trajectory and actual trajectory by learning algorithm using an artificial neural network. Generally, ANN has various weaknesses such as large training time, selection of neuron and hidden layer numbers required to deal with complex problem. To overcome these drawbacks, in this paper, the RBFN (radial basis function network) controller developed.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.4
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• pp.108-117
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• 2008

A transmission designed with P.T.O(Power Take-Off) axle for agricultural work vehicles including multi-purpose vehicles has been developed. It is focused on the 4-wheel drive transmission of synchronous contact type for practical use in fruit tree households which is required for a large-sized agricultural vehicle. Concerning to the specification performed, the load capacity is from 500kg to 1,000kg and the safety should be secured for passengers. In addition, the driving condition should also be secured under bad situations of the topographic slope, swampy land and the rest. In order to carry out above tests, a prototype vehicle through strength analysis of transmission design has been manufactured. Consequently, optimal design conditions on the power transmission with multi-purpose vehicle for various jobs are proposed such as an indication of optimal RPM and torque at a certain work situation. The performance test through the prototype of multi-purpose work vehicle is performed and the related data base is achieved. Finally, it is improved on troubles by the analysis of the results of R&D and provided the solutions on problems occurring to mass production in the future.

• Journal of the Korean Society of Mechanical Technology
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• v.13 no.3
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• pp.99-106
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• 2011

50kW급 동체회전형 파력발전시스템(WEC;wave energy converter)의 전력변환장치(PTO; power take-off)를 설계 제작한 후 성능시험을 하였다. 파력발전시스템은 2개의 실린더형 동체가 회전관절로 연결된 구조로 수면의 반정도 잠기는 구조로 되어있다. 파랑에 의해 유도된 회전관전의 움직임이 유압실린더에 힘을 가해주며, 유압실린더는 고압의 작동유를 축압기를 경유하여 발전기에 체결된 유압모터로 공급한다. 유압식 PTO은 유압실린더가 왕복운동하는 움직임을 이용하여 고품질의 전력을 생산하는데 효과전인 수단을 제공한다. 파력발전시스템의 경제성은 PTO의 에너지 변환 효율에 크게 의존한다. 발전기를 AC 380V 전력계통에 연계시킨 후, 발전기에서 나오는 출력이 5, 20, 35, 43kW 일때 PTO 전체와 개별기기에 대한 효율을 측정하였다. 본 논문에서 유압식 PTO시스템의 설계에 대해 설명하였으며 효율 향상에 초점을 맞추어 PTO 성능대해 분석하였다.

• Journal of Mechanical Science and Technology
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• v.15 no.6
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• pp.776-787
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• 2001

The turbofan engine performance analysis for a medium scale commercial aircraft was carried out and the LQR control scheme for performance optimization was studied. By using scaled component maps from well-known CF6 engine characteristics, the steady-state performance analysis result was compared with BR715-56 engine performance data. The transient performance analysis was performed with four fuel schedules. The linear simulation was done at the maximum take-off condition. The real time linear simulation was performed by interpolation of the system matrices, which used the least square method as the function of LPC rotational speed. By using linear system matrices of design point, the LQR controller which used control variables for the fuel flow and the LPC bleed air was designed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.5
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• pp.325-332
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• 2022

The vertical take-off and vertical landing (VTVL) function is essential to carry out exploration missions on the moon or Mars. For this, the engine of the exploration vehicle must have appropriate thrust control accuracy and response time. The hybrid rocket engine (HRE) is known to have a high level of thrust control capability that can satisfy these conditions. This study aims to first verify whether the thrust control performance of the developed HRE is suitable for VTVL. To this end, an oxidizer supply system that does not use a pressurization device was adopted, aiming for a mission time of about 10 seconds. In this study, the thrust control characteristics appearing under various supply pressure decreasing conditions were identified through experiments. Appropriate tank and charging conditions were set from the experimental results. In addition, the results of previous studies and current study's test were compared to confirm whether the developed HRE had adequate control performance for VTVL, and finally, the thrust control performance was verified through altitude control simulation.

• Proceedings of the Korea Institute of Convergence Signal Processing
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• 2003.06a
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• pp.82-85
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• 2003

This paper proposes a preprocessing method for tracking aircraft's take-off and lading. The method uses accumulative difference image technique for segmenting the object from the background, and obtains the centroid of the object exactly using centroid method. Then the moving object is analyzed and represented with the information such as feature point, velocity, and distance. A simulation result reveals that the proposed algorithm has good performance in segmenting and tracking the aircraft.

• Proceedings of the CALSEC Conference
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• 2004.02a
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• pp.60-64
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• 2004

The rapidly improving price-performance of wireless technologies is providing an unprecedented platform for the development of wireless applications for the business. Such applications are able to take advantage of a new paradigm of mobility for data services, with the ability to sensitize to location, time and personal features. While big business has been a central feature of wireless implementation, it is now clear that small- and medium-sized enterprises (SMEs) are beginning to take advantage of the strategic benefits of wireless data communications. This study examines the state-of-the-art of wireless data services in New Zealand. It provides a survey of 127 current applications in use, as well as two short illustrative cases of application use. The paper rounds off with a summary and conclusions.

• Journal of Korean Institute of Industrial Engineers
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• v.41 no.4
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• pp.330-337
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• 2015

A bucket-brigade is a way of transporting items where items are passed from one person to the next. The operation of the bucket brigade imitates the cooperative behavior of ants when brood, food or other resources are moved. Koo (2009) presented a bucket brigade-based assembly cell where each worker follows a simple rule: perform assembly operations on a product until the next worker downstream takes it over; then go back to the previous worker upstream to take over a new assembly job. In this way, the flow line is self-balanced without any predetermined job assignment. However, there are some productivity losses related to hand-off and blocking. This paper examines the hand-off and blocking losses and presents a new bucket brigade-based assembly cell where working areas for each assembler is restricted with the help of buffer interfaces. Simulation experiments are used to validate the performance of the new assembly system.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.26 no.2
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• pp.39-46
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• 2018

Departure Manager (DMAN) is a tool to optimize the departure sequence and to suggest appropriate take-off time and off-block time of each departure aircraft to the air traffic controllers. To that end, Variable Taxi Time (VTT), which is time duration of the aircraft from the stand to the runway, should be estimated. In this paper, a study for development of VTT prediction algorithm based on machine learning techniques is presented. The factors affecting aircraft taxi speeds were identified through the analysis of historical traffic data on the airport surface. The prediction model suggested in this study consists of several sub-models that reflect different types of surface maneuvers based on the analysis result. The prediction performance of the proposed method was evaluated using the actual operational data.