• 대한기계학회논문집A
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• 제37권8호
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• pp.1021-1027
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• 2013

원심펌프의 캐비테이션 침식에 대한 예측진단 기법을 본 연구에서 제시했다. 펌프의 침식 상태를 추정하기 위해 캐비테이션 소음을 측정하여 손상률을 계산하고 누적 손상은 특정 운전 상태에 따라 추정한 손상과 Miner의 법칙을 이용하여 계산했다. 펌프 임펠러의 잔존 유효 수명은 미래의 운전 조건을 가정한 누적 손상 예측치에 따라 계산하고 예측 불확도는 몬테카를로 모의를 통해 얻었다. 예측 및 시험 결과를 비교해 본 결과 개발된 방법이 캐비테이션 침식 상태와 잔존 유효 수명을 예측하는 데 적용될 수 있음을 확인할 수 있다.

• 산업공학
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• 제24권3호
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• pp.220-230
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• 2011

The multi-reservoir operation problem for efficient utilization of water resources involves conflicting objectives, and the problem can be solved by varying weight coefficient on objective functions. Accordingly, decision makers need to choose appropriate weight coefficients balancing the trade-offs among multiple objectives. Although the appropriateness of the weight coefficients may depend on the total amount of water inflow, reservoir operating policy may not be changed to a certain degree for different hydrological conditions on inflow. Therefore, we propose to use fuzzy Data Envelopment Analysis (DEA) to rank the weight coefficients in consideration of the inflow variation. In this approach, we generate a set of Paretooptimal solutions by applying different weight coefficients on Coordinated Multi-reservoir Operating Model. Then, we rank the Pareto-optimal solutions or the corresponding weight coefficients by using Fuzzy DEA model. With the proposed approach, we can suggest the best weight coefficients that can produce the appropriate Pareto-optimal solution considering the uncertainty of inflow, whereas the general DEA model cannot pinpoint the best weight coefficients.

• 조명전기설비학회논문지
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• 제23권7호
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• pp.29-40
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• 2009

This paper proposes a modeling and controller design approach for a hybrid wind power generation system that considers a fixed wind-turbine and a dump load. Since operating conditions are kept changing, it is challenge to design a control for reliable operation of the overall system To consider variable operating conditions, Takagi-Sugeno (TS) fuzzy model is taken into account to represent time-varying system by expressing the local dynamics of a nonlinear system through sub-systems, partitioned by linguistic rules. Also, each fuzzy model has uncertainty. Thus, in this paper, a modem nonlinear control design technique, the sliding mode nonlinear control design, is utilized for robust control mechanism In the simulation study, the proposed controller is compared with a proportional-integral (PI) controller. Simulation results show that the proposed controller is more effective against disturbances caused by wind speed and load variation than the PI controller, and thus it contributes to a better quality wind-hybrid power generation system.

• Nuclear Engineering and Technology
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• 제44권4호
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• pp.355-362
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• 2012

The aim of this study was to develop a bundle position-wise linear model (BPLM) to predict Pressure Tube (PT) diametral creep employing the previously measured PT diameters and operating conditions. There are twelve bundles in a fuel channel, and for each bundle a linear model was developed by using the dependent variables, such as the fast neutron fluences and the bundle coolant temperatures. The training data set was selected using the subtractive clustering method. The data of 39 channels that consist of 80 percent of a total of 49 measured channels from Units 2, 3, and 4 of the Wolsung nuclear plant in Korea were used to develop the BPLM. The data from the remaining 10 channels were used to test the developed BPLM. The BPLM was optimized by the maximum likelihood estimation method. The developed BPLM to predict PT diametral creep was verified using the operating data gathered from Units 2, 3, and 4. Two error components for the BPLM, which are the epistemic error and the aleatory error, were generated. The diametral creep prediction and two error components will be used for the generation of the regional overpower trip setpoint at the corresponding effective full power days. The root mean square (RMS) errors were also generated and compared to those from the current prediction method. The RMS errors were found to be less than the previous errors.

• 설비공학논문집
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• 제21권1호
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• pp.33-40
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• 2009

In the present experimental study, the pumping performances of diffuser/nozzle based piezoelectric micropumps are estimated with different operating factors and geometries. Here, the effects of the input voltage and frequency on the pumping performances have been examined together with the influences of the positions of the inlet and outlet. The results show that the flow rate of the micropump is larger with larger input voltage with the largest flow rates for the frequency to be close to 6.0 Hz all through the current experimental study. Also, it has been found that the positions of the inlet and outlet affect much on the performance of the piezoelectric micropumps. Error estimation has been carried out for the evaluation of the pumping performance in association with the uncertainty of the measurement.

• 한국항공운항학회지
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• 제21권3호
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• pp.55-64
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• 2013

As the price competition between airlines became increasingly intensified, due to increased participation of low-cost carriers in the air transport industry and the continued deregulation of international air transport, each airline has introduced various management techniques for securing international competitiveness and operational efficiency in order to cope with the uncertainty in air transport industry. The world leading LCCs, such as Ryan air, easyJet and Southwest, have changed their traditional business models by increasing operation to primary airports, diversifying operating routes, making strategic alliances with FSCs or other LCCs, increasing the operations on the mid or long distance routes, expanding ancillary revenues, etc. As Korea's air transport industry is confronting with intense competition, our LCCs are requested to adjust to this new challenging situation. As the world leading LCCs did, Korean LCCs are recommended to adopt new business models such as restructuring of the air transport industry through M&A, operating more flexibly in terms of frequency or route, launching of services to primary airports, making strategic alliances with foreign FSCs, developing of 4th or 6th traffic demands, etc.

• 항공우주시스템공학회지
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• 제13권5호
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• pp.57-64
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• 2019

항공전자 시스템은 유지비용 감소 및 운용성능 향상을 위하여 기능을 모듈화, 통합화 설계를 적용한 모듈 통합형 항공 전자 시스템으로 개발 되어지고 있으며, 다양한 임무 제어 수행을 위해서 가상화 기술을 적용한 파티셔닝 운용체제를 적용 하고 있다. 가상화 기술을 적용 할 경우 CPU 처리 부하 분배는 중요한 고려 대상이며, 특히 입출력 처리 시간에 대한 불확실성은 안정성 있는 항공전자 시스템 설계에 있어 위험 요소 중 하나이다. 본 논문에서는 유즈케이스를 통해 입/출력 처리 방식에 따르는 CPU 처리 부하량을 비교 분석하여 공간적/시간적 파티셔닝 예시에 적용함으로써 입/출력 처리 방식의 영향성을 검토하고자 한다.

• Nuclear Engineering and Technology
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• 제44권8호
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• pp.897-910
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• 2012

Inappropriate communications can cause a lack of necessary information exchange between operators and lead to serious consequences in large process systems such as nuclear power plants (NPPs). In this regard, various kinds of taxonomies of inappropriate communications have been developed to prevent inappropriate communications. However, there seems to be difficult to identify inappropriate communications from verbal protocol data between operators. Because the existing taxonomies were developed for use in report analysis, there is a problem of 'uncertainty'. In consequence, this paper proposes a new taxonomy of inappropriate communications and provides some insights to prevent inappropriate communications. In order to develop the taxonomy, existing taxonomies for four industries from 1980 to 2010 were collected and a new taxonomy is developed based on the simplified one-way communication model. In addition, the ratio of inappropriate communications from 8 samples of audio-visual format verbal protocol data recorded during emergency training sessions by operating teams is compared with performance scores calculated based on the task analysis. As a result, inappropriate communications can be easily identified from the verbal protocol data using the suggested taxonomy, and teams with a higher ratio of inappropriate communications tend to have a lower performance score.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2769-2774
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• 2007

In vacuum ejector-diffuser systems where a finite volume secondary chamber is used, the secondary jet exhibits transient characteristics during start-up. A steady state is achieved after some time in which mass entrainment prevails indefinitely inside the ejector, though there is no flow from the secondary chamber. An attempt is made in this work to study the infinite entrainment of secondary jet into the primary jet from a finite secondary chamber, with the help of a computational fluid dynamics method. The present study is also intended to identify the operating range of vacuum ejector-diffuser systems where the steady flow assumption can be applied without uncertainty. The results obtained show that the only condition in which an infinite mass entrainment is possible is the generation of a re-circulation zone near the primary nozzle exit. The flow in the secondary chamber attains a state of dynamic equilibrium at this point. Steady flow assumption is valid only after this point.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 춘계학술대회 논문집
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• pp.423-426
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• 2011

The excessive axial load occurred in an immovable zone of continuous welded rail(CWR) tracks threatens the security of running trains due to the track buckling in extreme hot summer. The influence factors, such as rail temperature for compressive stress, ballast resistance for track stiffness and initial imperfection of track for tracks irregularity are uncertain track parameters that are randomly varied by climate conditions, operating conditions and maintenance of track etc. So, buckling of CWR tracks has very high uncertainties. Therefore, applying the probabilistic approach method is essential in order to rationally consider the uncertainty and randomness of the various parameters. In this study, buckling sensitivity analysis was carried out with respect to the characteristics of probability distribution of lateral ballast resistance using the buckling probability evaluation system of CWR tracks developed by our research team.