• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.15 no.7
• /
• pp.4692-4697
• /
• 2014

A micro-grid including photovoltaic source and Li battery has been installed and operated for several years at the campus of USF and been used as a test bed. Photovoltaic power source has been strongly influenced by the location, weather and climate of the installed area. To compensate for the uncertainty of photovoltaic source's power output, a Li battery is connected directly to the photovoltaic source and supplies electric power to the grid. The Li battery is operated to supply power output to the grid according to the charging or discharging mode of the battery based on the average power output of the photovoltaic source, which is calculated from the monitored data for several years. The grid of the photovoltaic and Li battery system is operated as a severe loading condition and the operating characteristics of PV source and Li battery cells are analyzed in detail.

• Journal of Environmental Impact Assessment
• /
• v.14 no.4
• /
• pp.227-235
• /
• 2005

Source contribution for VOCs collected in Seoul metropolitan area was conducted using PAMs (Photochemical assessment monitoring system) data and CMB(Chemical Mass Balance) model8.0, in order to estimate spatial and temporal variations of VOCs source contribution in that area, and also to compare with corresponding emission inventory. VOCs data used in model calculation were collected at 6 different sites of PAMs(Seokmori, Guwoldong, Simgokdong, Bulgwangdong, Jeongdong and Yangpyeong) and 22 out of 56 VOCs species were analyzed from June 2002 to march 2003 and used for CMB model estimation. The result showed that vehicle exhaust, coating and energy combustion were important sources of VOCs in Seoul metropolitan area, averaging 32.6%, 25.5% and 25.1%, respectively. In this study as well as other references, it was revealed that vehicle exhaust is the main contributor of urban area VOCs, but there is remarkable contrast between emission inventory and model estimation. Vehicle exhaust portion is seriously underestimated while coating is usually overestimated in emission estimates, compared to CMB results. Therefore, it is considered to assert and confirm the uncertainty of emission estimates and clarify the distinction between two other source apportionment methods.

• 제어로봇시스템학회:학술대회논문집
• /
• 2003.10a
• /
• pp.537-541
• /
• 2003

In order to control the missiles by aerodynamics, control surfaces sometime called fins are used. Deflection angles of these fins are the right control variables of the aerodynamics, but aerodynamicists prefer to use analytic variables called aileron, elevator and rudder instead of these physical variables, because these three analytic variables dominantly influence on the roll, pitch and yaw channels of the missile maneuver, respectively, and each can be assumed a linear combination of four fin deflection angles. On that basis, roll, pitch and yaw autopilots for controlling the attitudes or lateral acceleration of the missile are designed, and as a consequence outputs of each autopilot are aileron, elevator and rudder commands, respectively. In the existing fin control scheme for the typical tail-fin controlled cruciform missiles, firstly these outputs are distributed to four fin defection commands, and after that four fins are actuated by fin controllers so that their deflections follow the commands. This paper shows that performance of such control schemes can be degraded significantly when fin actuators have certain physical constraints such as slew rate, voltage or current limit, uncertainty of actuator dynamics, and so on, and propose a new control scheme which alleviates such problems. This scheme can be widely applied to various fin actuation systems. But in this paper, for convenience, tail-fin controlled cruciform missile is taken as an example, and it is shown that a proposed control scheme gives better performance than the existing one.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.28 no.4
• /
• pp.343-350
• /
• 2015

Extensive discussion on the optimal types of offshore wind turbine(OWT) among monopile, tripod and jacket in the intermediate depth of water has been actively carried out in worldwide wind turbine industry. Selecting the optimal types of OWT among several substructural types, it is required to consider the economic and technical feasibility including dynamically stable design of a wind turbine system. In this study, the effects of loading levels and uncertainties of soil properties on the natural frequency of OWT have been quantitatively investigated. In conclusion, the natural frequency of monopile-type OWTs has a significant level of uncertainty, hence it is very important to minimize the level of uncertainties in soil properties when the monopile is selected as a foundation for an OWT.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.45 no.11
• /
• pp.15-22
• /
• 2008

The cdma2000 1xEV-DO system controls the data rates of mobile terminals based on a binary overload indicator from the base station and a simple probabilistic model. However, this control scheme has difficulty in predicting the future behavior of mobile terminals due to a probabilistic uncertainty and has no reliable means of suppressing the traffic overload, which may result in performance degradation of CDMA systems that have interference-limited capacity. This Paper proposes a new traffic control scheme that controls the data rates of mobile terminals effectively by predicting the future traffic load and adjusting the forward-link control channel. The proposed scheme is analyzed by modeling it as a multi-dimensional Markov process and compared with conventional schemes. The numerical results show that the maximum cell throughput of the proposed scheme is much higher than those of the conventional schemes.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.20 no.1
• /
• pp.19-25
• /
• 2020

In frequent pattern mining, the uncertainty of each item is accompanied by a loss of information. AAlso, in real environment, the importance of patterns changes with time, so fuzzy logic must be applied to meet these requirements and the dynamic characteristics of the importance of patterns should be considered. In this paper, we propose a fuzzy utility mining technique for extracting frequent web page sets from web log databases through fuzzy utility-based web page set mining. Here, the downward closure characteristic of the fuzzy set is applied to remove a large space by the minimum fuzzy utility threshold (MFUT)and the user-defined percentile(UDP). Extensive performance analyses show that our algorithm is very efficient and scalable for Fuzzy Utility Mining using dynamic weights.

• Journal of Korean Society on Water Environment
• /
• v.35 no.6
• /
• pp.481-496
• /
• 2019

The Ministry of Environment has measured streamflow at eight-day intervals for the estimation of standard flow of the Total Maximum Daily Loads (TMDL) system. This study identified the availability of the partially measured the eight-day interval data for estimating standard flow and found the optimal extension techniques of standard flow. The study area was selected for the Nakbon-A watershed in the Nakdong River, and four streamflow record extension techniques of standard flow were considered: extension, percentile, drainagearea, and regional regression methods. The flow duration curve (FDC) using the eight-day interval streamflow data indicated very high Nash and Sutcliffe Efficiency (NSE) values above 90 % from FDC-II to FDC-VII compared to FDC-VIII, the standard FDC. This result demonstrates that FDC using daily data of three-six cumulative years could represent standard FDC fairly well. For the streamflow record extension techniques of standard flow, the percentile method was selected as the optimal alternative, showing the minimal difference from FDC-VIII. These results validate the availability of the eight-day interval streamflow data in the standard flow estimation and the application of extension techniques. It seems that these results could reduce the uncertainty of partially measured streamflow data for water quantity and quality management.

• Journal of Computational Design and Engineering
• /
• v.3 no.3
• /
• pp.179-190
• /
• 2016

A kind of modified epoxy resin sheet molding compounds of the impeller has been designed. Through the test, the non-metal impeller has a better environmental aging performance, but must do the waterproof processing design. In order to improve the stability of the impeller vibration design, the influence of uncertainty factors is considered, and a multi-objective robust optimization method is proposed to reduce the weight of the impeller. Firstly, based on the fluid-structure interaction, the analysis model of the impeller vibration is constructed. Secondly, the optimal approximate model of the impeller is constructed by using the Latin hypercube and radial basis function, and the fitting and optimization accuracy of the approximate model is improved by increasing the sample points. Finally, the micro multi-objective genetic algorithm is applied to the robust optimization of approximate model, and the Monte Carlo simulation and Sobol sampling techniques are used for reliability analysis. By comparing the results of the deterministic, different sigma levels and different materials, the multi-objective optimization of the SMC molding impeller can meet the requirements of engineering stability and lightweight. And the effectiveness of the proposed multi-objective robust optimization method is verified by the error analysis. After the SMC molding and the robust optimization of the impeller, the optimized rate reached 42.5%, which greatly improved the economic benefit, and greatly reduce the vibration of the ventilation system.

• Journal of Korea Water Resources Association
• /
• v.50 no.1
• /
• pp.17-28
• /
• 2017

A recent increase in extreme weather events and flash floods associated with the enhanced climate variability results in an increase in climate-related disasters. For these reasons, various studies based on a high resolution weather radar system have been carried out. The weather radar can provide estimates of precipitation in real-time over a wide area, while ground-based rain gauges only provides a point estimate in space. Weather radar is thus capable of identifying changes in rainfall structure as it moves through an ungauged basin. However, the advantage of the weather radar rainfall estimates has been limited by a variety of sources of uncertainty in the radar reflectivity process, including systematic and random errors. In this study, we developed an ensemble radar rainfall estimation scheme using the multivariate copula method. The results presented in this study confirmed that the proposed ensemble technique can effectively reproduce the rainfall statistics such as mean, variance and skewness (more importantly the extremes) as well as the spatio-temporal structure of rainfall fields.

• Journal of Korean Society of Industrial and Systems Engineering
• /
• v.39 no.4
• /
• pp.72-80
• /
• 2016

The market size of plant projects in overseas is so large that domestic EPC project contractors are actively seeking the overseas projects and then trying to meet completion plans since successful fulfillment of these projects can provide great opportunities for them to expand into new foreign markets. International EPC projects involve all of the uncertainties common to domestic projects as well as uncertainties specific to foreign projects including marine transportation, customs, regulations, nationality, culture and so on. When overseas project gets off-schedule, the resulting uncertainty may trigger unexpected exceptions and then critical effects to the project performance. It usually require much more time and costs to encounter these exceptions in foreign sites compared to domestic project sites. Therefore, an exception handling approach is required to manage exceptions effectively for successful project progress in foreign project sites. In this research, we proposed a methodology for prediction and evaluation of exceptions caused by risks in international EPC projects based on sensitivity analysis and Bayesian Networks. First, we identified project schedule risks and related exceptions, which may meet during the fulfillment of foreign EPC projects that is performed in a sequence of engineering, procurement, preparatory manufacture, foreign shipping, construction, inspection and modification activities, and affect project performance, using literature review and expert interviews. The impact of exceptions to the schedule delay were also identified. Second, we proposed a methodology to predict the occurrence of exceptions caused by project risks and evaluate them. Using sensitivity analysis, we can identify activities that critically affect schedule delay and need to focus by priority. Then, we use Bayesian Networks to predict and evaluate exceptions. Third, we applied the proposed methodology to an international EPC project example to validate the proposed approach. Finally, we concluded the research with the further research topics. We expect that the proposed approach can be extended to apply in exception management in project management.