• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.7
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• pp.118-126
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• 2003

In this study, a battery charge and discharge regulator of modular type is designed as paralleled bi-directional converter that is possible to provide the power without failure not only in the steady state but also in the transient period by the step load variation or the unexpected faults among the converter modules. Each converter module is designed to get stability, performance, reliability, and maintainability and the average current mode method used for controller has the advantages such as noise immunity, fast response, and the real average current signal acquisition. The equivalent model and small signal model for the paralleled battery chargerIdischarger are presented, and also the transfer functions are analyzed for the CCM(Continuous Charge Mode), CDM(Continuous Discharge Mode) and DDM(Discontinuous Discharge Mode). The experiments of the paralleled bi-directional converter are carried out in the step load variation, and in faults of one converter module respectively. And the performance of paralleled bi-directional converter is verified via the experimental results.

• Aerospace Engineering and Technology
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• v.7 no.1
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• pp.83-90
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• 2008

The next generation LID satellite has 64KB PROM which contains the boot loader and the monitor software, and two 4MB NVMEMs which are used for flight software storage. The boot loader has two operation modes which are the flight software mode and the monitor mode. In the flight software mode, it checks CRC checksum of selected NVMEM and copies flight software image from NVMEM to RAM And then it starts VxWorks RTOS in RAM, creates flight software tasks, and starts execution of flight software. In the monitor mode, it activates monitor software which performs NVMEM reprogramming and board-level testing on the ground. This paper is to present the design of Boot ROM software and verification method using simulator.

• Journal of the Korea Society of Computer and Information
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• v.24 no.11
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• pp.29-39
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• 2019

As mobile robot applications increase in real life, the need of low cost autonomous driving are gradually increasing. We propose a novel vision-based real-time lane detection and tracking system that supports autonomous driving of mobile robots in constrained tracks which are designed considering indoor driving conditions of mobile robots. Considering the processing of lanes with various shapes and the pre-adjustment of operation parameters, the system structure with multi-operation modes are designed. In parameter tuning mode, thresholds of the color filter is dynamically adjusted based on the geometric property of the lane thickness. And in the unstable input mode of curved tracks and the stable input mode of straight tracks, lane feature pixels are adaptively extracted based on the geometric and temporal characteristics of the lanes and the lane model is fitted using the least-squared method. The track centerline is calculated using lane models and the motion model is simplified and tracked by a linear Kalman filter. In the driving experiments, it was confirmed that even in low-performance robot configurations, real-time processing produces the accurate autonomous driving in the constrained track.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.147-147
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• 2016

최근 기후변화로 인한 기상이변이 빈번히 발생하면서 그로 인한 피해도 점점 증가하고 있다. 이를 최소화하기 위해서는 기후변화가 강수에 미치는 영향에 대한 연구가 필요하며, 특히 강수의 기후변화를 고려한 장기적인 변동에 대한 예측이 매우 중요하다. 그 중, 기후변화로 인한 강수현상의 변화를 분석하기 위한 방법 중 하나로 강수 현상이 주변 기후 요소의 분포에 영향을 받는다는 가정 하에 기상인자를 통하여 강수를 예측하는 방법이 있다. 우리나라에 영향을 미치는 주변 기상인자들과 강수 간의 상관관계를 분석하여 상관관계가 높게 나타나는 기상인자를 통해 우리나라 강수량을 예측하면 장기적인 관점에서 강수 예측의 정확도를 높일 수 있다. 하지만 상관관계 분석에 있어서 강수 원 자료 와 기상인자간의 상관관계를 비교할 경우 원 자료가 가지는 큰 변동성으로 인해 정확한 상관관계 분석이 이루어지지 않을 가능성이 크다. 따라서 강수자료를 분해하여 분해된 요소별로 상관관계를 분석하여 분석의 정확도를 높일 필요가 있다. 다양한 자료 분해 방법중 경험적 모드분해법(Empirical Mode Decomposition, EMD)을 사용할 경우 자료의 분해에 있어서 주기성, 경향성에 따라 분해가 가능하며, 비정상성을 가지고 있는 시계열에 대해 효과적으로 분해가 가능한 장점이 있다. 본 연구에서는 30년 이상의 자료기간을 가지는 지점의 강수량 자료를 바탕으로 경험적 모드분해법을 이용하여 강수자료를 분해하고, 이를 다양한 기상인자와의 상관관계를 분석함으로써, 우리나라 강수량 변동과 연관이 있는 기상인자들을 선별하였다. 선별된 기상인지를 바탕으로 다중회귀분석을 수행하여 기상인자를 독립변수로 하는 강수 예측식을 구축하여 우리나라 강수의 예측 가능성을 살펴보고자 한다.

• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.4
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• pp.84-90
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• 2004

A performance evaluation is made in terms of thrust, impulse bit. and specific impulses for a set of mono-propellant hydrazine thrusters producing 0.95 lbf of nominal thrust at an inlet pressure of 350 psia. With a brief description on the hot-firing test configuration and procedures. a typical data obtained from steady-state firing mode is given directly showing the variational behavior of propellant supply pressure, mass flow rate, vacuum condition, and thrust. The performance features are successfully compared to the reference criteria of 1-lbf standard mono-propellant rocket engine. Additionally. a statistical inter-thruster treatment is concisely depicted for the justification of selected thrusters as a grouped member of flight model for spacecraft propulsion system.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.877-880
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• 2017

Impeller blades in the centrifugal compressor are subjected to static loads due to the high-speed rotation and steady aerodynamic forces. At the same time, aerodynamic excitations by the interaction between the impeller and the diffuser vanes(DV) periodically excite the impeller blades in resonant conditions, which may lead to high cycle fatigue (HCF) and eventually result in failure of the blades. In order to predict the structural response accurately, the aerodynamic excitation and the major resonant conditions were predicted by performing the unsteady flow analysis and modal analysis using ANSYS. Next, a unidirectional forced vibration analysis was performed by using fluid-structure interaction (FSI) method, and the safety of HCF was evaluated based on the results.

• Proceedings of the Korea Information Processing Society Conference
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• 2012.11a
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• pp.8-10
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• 2012

위성을 전체적으로 제어하는 탑재소프트웨어가 동작하는 주 메모리와는 별도로 세이프가드 메모리가 있다. 세이프가드 메모리는 주로 위성의 장애관리를 위해 사용되는 것으로 프로세서 리셋 시에 전체적으로 초기화가 수행되는 주 메모리와는 달리 별도의 전원을 사용하여 항상 Power-ON 상태를 유지하고 주/부 2개의 메모리가 주/부 프로세서와 Cross-Strap으로 연결되어 어느 프로세서에서든 접속이 가능하도록 구성되어 있다. 위성에 심각한 장애가 발생하여 정상적인 운영이 불가능한 경우, 위성은 Fail-over 과정을 거치게 되는데, Fail-over 과정에서 2개의 세이프가드 메모리의 비상운영데이터 영역에 장애 발생원인 및 프로세서 리셋 이후에 필요한 정보들을 기록하고, 미리 정해진 Backup 하드웨어를 이용하여 시스템 초기화가 수행된다. Backup 하드웨어를 통하여 프로세서가 정상적으로 Boot-up되면 세이프가드 메모리에 저장된 비상운영데이터를 이용하여 위성의 장애발생 원인을 파악하고, 정상운영모드로 복귀하는 절차를 거치게 된다. 본 논문은 저궤도 위성에서 사용되는 세이프가드 메모리 운영방식에 대해 기술한 것이다.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.17 no.2
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• pp.130-137
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• 2012

The underwater glider using conception of Lagrangian method, is a new observation platform to understand the properties of the ocean vertically. In 2011 March, KORDI made a first successful autonomous trip from Hupo to west coast of Uleungdo piloting Littoral Glider of Alaska Native Technology LLC. The journey considered many environmental variables and route vigilantly selected, the glider covered 177 km horizontally and took approximately 6 days (153 hours). Despite the existence of 1 kt eddy current, Sound velocity sampling was conducted from 5 meters and reaching maximum of 200 meters depth at each dive. It successfully collected sound velocity and temperature profile at every 5 seconds totaling up to 1408 profiles using SVT&P sensor. During the flight it was also a mission to check the diverse modes of the glider i.e. spiral, waypoints, heading, drift and hover could function without a defect in a given situation. These modes were thoroughly monitored and it could be considered that the glider handled it well during the flight. As a result of this test flight, it was evident that the given underwater glider could operate under 2kt current environment with users defined heading and depth, also with the payload up to 5 kg without changing internal buoyancy.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.6
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• pp.357-365
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• 2022

Refrigerant mischarging is one of the most frequently occurring failure modes in air conditioners, and both undercharging and overcharging degrade cooling performance. Therefore, it is important to accurately determine the amount of charged refrigerant. In this study, a support vector machine (SVM) model was developed to multi-classify the refrigerant mischarge through steady-state identification via fuzzy clustering techniques. For steady-state identification, a fuzzy clustering algorithm was applied to the air conditioner operation data using the difference between moving averages. The identification results using the proposed method were compared with those using existing steady-state determination techniques studied through the inversed Fisher's discriminant ratio (IFDR). Subsequently, the main features were selected using minimum redundancy maximum relevance (mRMR) considering the correlation among candidate features, and an SVM multi-classification model was devised using the derived features. The proposed method achieves satisfactory accuracy and robustness from test data collected in the new domain.

• KIPS Transactions on Computer and Communication Systems
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• v.4 no.2
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• pp.47-56
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• 2015

In an energy saving server cluster environment, the power modes of servers are controlled according to load situation, that is, by making ON only minimum number of servers needed to handle current load while making the other servers OFF. This algorithm works well under normal circumstances, but does not guarantee QoS under abnormal circumstances such as sharply rising or falling loads. This is because the number of ON servers cannot be increased immediately due to the time delay for servers to turn ON from OFF. In this paper, we propose a new prediction algorithm of the power consumption for improving QoS under not only normal but also abnormal circumstances. The proposed prediction algorithm consists of two parts: prediction based on the conventional time series analysis and prediction adjustment based on trend analysis. We performed experiments using 15 PCs and compared performance for 4 types of conventional time series based prediction methods and their modified methods with our prediction algorithm. Experimental results show that Exponential Smoothing with Trend Adjusted (ESTA) and its modified ESTA (MESTA) proposed in this paper are outperforming among 4 types of prediction methods in terms of normalized QoS and number of good reponses per power consumed, and QoS of MESTA proposed in this paper is 7.5% and 3.3% better than that of conventional ESTA for artificial load pattern and real load pattern, respectively.