• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.6
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• pp.98-104
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• 2015

Excessive thrust acting on the rotor of pump can cause the damage of pump or the decrease of pump lifetime. Therefore, for ensuring the safety of LOX pump of a liquid rocket engine, the thrust of pump rotor is estimated by similarity tests. Axial thrust is indirectly measured by an axial thrust measurement unit positioned outside pump. Radial thrust is calculated based on pressure distribution of volute scroll. As a result, axial and radial thrust are increased when the flowrate of pump decreases. However, both thrusts do not affect the stability of pump rotor since their values are not large.

• Proceedings of the KSR Conference
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• 2006.11b
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• pp.624-630
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• 2006

This paper studies a modeling to demonstrate predicted reliability of the train control system components by performing an accelerated stress test. There are two tests for demonstrating predicted reliability; test run at the whole system level, and accelerated life test and accelerated stress test at the component level. In this paper, we imposed accelerated stress on the system and studied the train control system modeling for the accelerated stress test, which demonstrates predicted reliability according to whether or not the equipment is operating. Reliability of train control system consisting of electronic components varies drastically according to temperature so we considered the Arrhenius equation and the activation energy of electronic components. We also used reliability modeling with weighted average and calculated time necessary to complete the accelerated stress test on train control system.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2015.10a
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• pp.232-235
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• 2015

In recent years, mobile devices are equipped with functionalities comparable to those computers. However, mobile devices have limited resources due to constraints, such as low processing power, limited memory, unpredictable connectivity, and limited battery life. To enhance the capacity of mobile devices, an interesting idea is to use cloud computing and virtualization techniques to shift the workload from mobile devices to a computational infrastructure. Those techniques consist of migrating resource-intensive computations from a mobile device to the resource-rich cloud, or server (called nearby infrastructure). In order to achieve their goals, researchers designed mobile cloud applications models (examples: CloneCloud, Cloudlet, and Weblet). In this paper, we want to highlight on cloudlet architecture (nearby infrastructure with mobile device), its methodology and discuss about the impact of distance between cloudlet and mobile device in our work design.

• JOURNAL OF ELECTRICAL WORLD
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• s.302
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• pp.64-70
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• 2002

현재 미쓰비시(삼릉)전기를 비롯한 빌딩관련업계에서는 빌딩의 재건축이나 설비투자는 감소되고 건물$\cdot$설비의 장(長)수명화가 도모되고 있으며, 전체수명에 걸친 경제적 부담을 종합적으로 억제함으로써 러닝코스트를 최적화하려는 경향은 더욱 높아질 것으로 예측된다. 빌딩의 기획$\cdot$설계단계에서부터 폐기까지의 라이프사이클에서 러닝코스트가 점하는 비율은 라이프사이클 코스트(LCC)전체의 $70\%$에서 $80\%$가 된다. 이것을 억제하는 것은 중요한 과제로서, 그 지원시스템으로 고도의 빌딩매니지먼트 시스템(BMS)이 필요하게 된다. 개발한 BMS는 중$\cdot$대규모 빌딩시스템 확대판매를 위한 새로운 시스템이지만 종합관리서비스를 위한 수탁용 지원시스템이기도 하다. 빌딩 라이프사이클의 전(全)단계(기획$\cdot$설계$\rightarrow$건설$\rightarrow$운용관리$\rightarrow$처분)에서 대응하게 되어 있다. 동사그룹(미쓰비시전기 및 미쓰비시전기 빌딩테크노서비스)은 빌딩오너의 경영적 시각에서, 활동이 가능하며 메이커와 서비스회사의 구분없이 다방면에 걸쳐 역할을 담당하고 있다. 또 고객에게 가치를 제공하는 기술과 전국적인 대응체제는 BMS 개발에 큰 힘이 되고 있다. 개발한 BMS의 특징은, 지금까지의 설비관리시스템의 실적을 베이스(경험, 노하우 등)로 다시 보완하여 장치함으로써 임차인관리시스템, 나아가 에너지 절약 요구에 응한 에너지관리까지 확대하여 유기적(관련정보와 연계를 갖도록 한다는 의미)으로 구축한 시스템을 완성한 점이다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2010.05a
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• pp.860-863
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• 2010

Wireless sensor networks consist of small, autonomous devices with wireless networking capabilities. In order to further increase the applicability in real world applications, minimizing energy consumption is one of the most critical issues. Therefore, accurate energy model is required for the evaluation of wireless sensor networks. In this paper, we analyze the energy consumption for wireless sensor networks. To estimate the lifetime of sensor node, we have measured the energy characteristics of sensor node based on Telosb platforms running TinyOS. Based on the proposed model, the estimated lifetime of a battery powered sensor node can use about 6.925 months for 10 times motion detection per hour.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.4
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• pp.1495-1501
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• 2011

Fatigue life and vibration can be analyzed at automotive propeller shaft during driving in this study. The york part is shown with the maximum equivalent stress and displacement of $1.3177{\times}10^3$Pa and $3.6148{\times}10^{-4}$m. The possible life in use in case of 'SAE bracket' is the shortest among the fatigue loading lives of 'SAE bracket', 'SAE transmission' and Sample history. There are the most frequency as 80% in case of 'SAE bracket and the least frequency as 5% in case of Sample history'. Maximum amplitude displacement is 0.00261m at 58 Hz at forced vibration. As the result of this study is applied by the propeller shaf, the prevention on fatigue damage and the durability are predicted.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.4
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• pp.939-949
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• 2017

Prognostics and health management(PHM) is actively utilized by industry as an essential technology focusing on accurately monitoring the health state of a system and predicting the remaining useful life(RUL). An effective PHM is expected to reduce maintenance costs as well as improve safety of system by preventing failure in advance. With these advantages, PHM can be applied to the battery system which is a core element to provide electricity for devices with mobility, since battery faults could lead to operational downtime, performance degradation, and even catastrophic loss of human life by unexpected explosion due to non-linear characteristics of battery. In this paper we mainly review a recent progress on various models for predicting RUL of battery with high accuracy satisfying the given confidence interval level. Moreover, performance evaluation metrics for battery prognostics are presented in detail to show the strength of these metrics compared to the traditional ones used in the existing forecasting applications.

• Journal of the Korean Electrochemical Society
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• v.19 no.1
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• pp.14-20
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• 2016

Vanadium redox flow battery (VRFB) is an energy conversion device in which charging and discharging are alternatively carried out by oxidation and reduction reactions of vanadium ions with different oxidation states. VRFB consists of electrolyte, electrode, ion-exchange membrane, etc. The role of ion-exchange membranes in VRFB separates anolyte and catholyte and provides a high conductivity to hydrogen ions. Recently much attention has been devoted to develop ideal ion-exchange membranes for VRFB. A number of developed ion-exchange membranes should be evaluated to find out ideal ion-exchange membranes for VRFB. Long-term durability test is a crucial characterization of ion-exchange membranes for commercialization, but is very time-consuming. In this study, the life time prediction protocol of ion-exchange membranes in VRFB cell tests was developed through short-term single cell performance evaluation (real total operation time, 87.5 hrs) at three different current densities. We confirmed a decrease in test time up to 96.2% of real durability tests (expected total operation time, 2,296 hrs) and 5~6% of relative error discrepancy between the predicted and the real life time in a unit cell.

• Journal of Korean Ophthalmic Optics Society
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• v.13 no.4
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• pp.89-94
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• 2008

Purpose: To observe the high temperature creep test and the fracture surface of the samples of 9% Ni alloy steel generally used for all kinds of mahine parts and predict the durability of that by determining a constant of C with a Larson-Miller variable. Methods: The equipment of this test was made into lever-beam style designed by Andrade and F. Garofalo et al.. The condition of creep test was set under 16 kinds of conditions after fixing 4 kinds of temperature condition and 4 kinds of stress condition to check how it effects the samples. Results: The temperature of creep test was increased, the stress index (n) of creep deformation was gradually decreased from 3.97 to 3.55. The activation energy of creep deformation was decreased from 90.39 to 83.64 kcal/mol when the stress was increased. A constant of C value by calculation of larson-Miller variable was about 22 and if temperature for use is suggested, the durability could be calculated. Conclusions: By analyzing the fracture phenomenon and suggesting the observation result of the fracture surface of the samples and creep test of 9% Ni alloy steel, the basic design data for the practical use of accessories in the field of equipment could be constructed and used to predict the durability of the equipment.

• The Transactions of the Korean Institute of Power Electronics
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• v.13 no.4
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• pp.247-256
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• 2008

Regenerative energy generated by regenerative braking of DC traction can cause the system malfunction or damage to the rectifier, or malfunction of the power conversion device in power supply system by DC Line voltage rise in feeder line. Regenerative energy storage system using super capacitor is one of the ways to stabilize DC line voltage. In this paper, energy storage system of DC traction system using super-capacitor bank is implemented and using the field measurement data of the station N and the station S on the Line 2, the operation characteristics of line voltage caused by regenerative energy of electric trains are verified. Also, charge/discharge characteristics of super capacitor are verified as well. Thus, we can verify the operation characteristics of super-capacitor bank for regenerative energy storage system installed in DC Traction. And if we can use field measurement data of DC line voltage, we have obtained cost reduction. The stabilization of the system will be improved by measuring the operation characteristics of regenerative energy storage system in certain section operated by DC traction and predicting the capacity and lifetime of super-capacitor.