• Transactions of the Korean hydrogen and new energy society
• /
• v.16 no.4
• /
• pp.364-371
• /
• 2005

Fuel cell systems(FCS) have a financial and environmental advantage by providing electricity at a high efficiency and useful heat. For use in a residence, a polymer electrolyte fuel cell system(PEFCS) with a battery pack and a hot water storage tank has been modelled and simulated. The system is operated without connection to grid line. Its electric conversion efficiency and heat recovery performance are highly dependent on operation strategies and also on the seasonal thermal and electric load pattern. The output of the fuel cell is controlled stepwise as a function of the state of the battery and/or the storage water tank. In this study various operation strategies for cogeneration fuel cell systems are investigated. Average fuel saving rates at different seasons are calculated to find proper load management strategy. The scheme can be used to determine the optimal operating strategies of PEFCS for residential and building applications.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.27 no.10C
• /
• pp.921-932
• /
• 2002

In this research, we seek to identify an effective operation management strategy of telecommunication systems. In order to develop operation management strategies, we implement a quantitative techno-economic analysis. We evaluate related issues and factors, and apply the developed method to PSTN switching systems. In the proposed techno-economic modeling, we apply a well-known factor analysis technique-analytic hierarchy process-to evaluate PSTN operation management strategies. Then, we implement a decision analysis methodology to evaluate the cost of proposed strategies. We evaluate the proposed methodology by using available real data of the PSTN system. The primary impact of this research will be realized in helping PSTN operator select the best operation management strategy of PSTN system.

• Membrane and Water Treatment
• /
• v.9 no.6
• /
• pp.421-434
• /
• 2018

Decision-makers have different and sometimes conflicting goals with utilities in operating dam reservoirs. As repeated interactions exist between decision-makers in the long-term, and the utility of each decision-making organization is affected not only by its selected strategy, but also by other rivals' strategies; selecting and prioritizing optimum strategies from a decision maker's point of view are of great importance while interacting with others. In this paper, a model based on a fuzzy set theory, for determining the priority of decision-makers' strategies in optimal qualitative-quantitative operation management of dam reservoir is presented. The fuzzy priority matrix is developed via defining membership functions of a fuzzy set for each decision maker's strategies, so that all uncertainties are taken into account. This matrix includes priorities assigned to possible combination for other decision makers' strategies in bargaining with each player's viewpoint. Here, the 15-Khordad Dam located in the central part of Iran, suffering from low water quality, was studied in order to evaluate the effectiveness of the model. Then, the range of quality of water withdrawal agreed by all decision-makers was determined using the prioritization matrix based on fuzzy logic. The results showed that the model proposed in the study had high effectiveness model.

• International Journal of Highway Engineering
• /
• v.20 no.2
• /
• pp.109-118
• /
• 2018

PURPOSES : This study evaluates the efficiency of snow removal operation resources using data envelopment analysis (DEA). The results of this study can help decision-making strategies, especially for resource allocation for snow removal works on national highways. METHODS : First, regional road management offices (DMUs) for efficiency evaluation were set up, and a database (for years 2012-2016) for analysis was formed. Second, DEA was carried out by selecting input and output variables based on the constructed database. Lastly, based on the results of the DEA, the efficiency of each regional road management office was evaluated. In addition, the potential for future improvement was determined. RESULTS : The results showed that there was a large variation in efficiency of snow removal operation resources by regional offices. CONCLUSIONS : The results of this study imply that the evaluation of efficiency for snow removal operation resources is important when decisions related to snow-removal strategies are made by road management offices.

• Nuclear Engineering and Technology
• /
• v.54 no.8
• /
• pp.2840-2851
• /
• 2022

Electric boilers (EBs) are the backup steam source for the auxiliary steam system of high-temperature gas-cooled reactor nuclear power plants. When the plant is in normal operations, the EB is always in hot standby status. However, the current hot standby operation strategy has problems of slow response, high power consumption, and long operation time. To solve these problems, this study focuses on the optimization of hot standby operations for the EB system. First, mathematical models of an electrode immersion EB and its accompanying deaerator were established. Then, a control simulation platform of the EB system was developed in MATLAB/Simulink implementing the established mathematical models and corresponding control systems. Finally, two optimization strategies for the EB hot standby operation were proposed, followed by dynamic simulations of the EB system transient from hot standby to normal operations. The results indicate that the proposed optimization strategies can significantly speed up the transient response of the EB system from hot standby to normal operations and reduce the power consumption in hot standby operations, improving the dynamic performance and economy of the system.

• Advances in Energy Research
• /
• v.4 no.1
• /
• pp.87-106
• /
• 2016

In this research, optimum design of the combined solar collector, geothermal heat pump and thermal seasonal storage system for heating and cooling a sample greenhouse is studied. In order to optimize the system from technical point of view some new control strategies and functions resulting from important TRNSYS output diagrams are presented. Temperatures of ground, rock bed storage, outlet ground heat exchanger fluid and entering fluid to the evaporator specify our strategies. Optimal heat storage is done with maximum efficiency and minimum loss. Mean seasonal heating and cooling COPs of 4.92 and 7.14 are achieved in series mode as there is no need to start the heat pump sometimes. Furthermore, optimal parallel operation of the storage and the heat pump is studied by applying the same control strategies. Although the aforementioned system has higher mean seasonal heating and cooling COPs (4.96 and 7.18 respectively) and lower initial cost, it requires higher amounts of auxiliary energy either. Soil temperature around ground heat exchanger will also increase up to $1.5^{\circ}C$ after 2 years of operation as a result of seasonal storage. At the end, the optimum combined system is chosen by trade-off between technical and economic issues.

• Journal of the Korea Society for Simulation
• /
• v.31 no.3
• /
• pp.23-34
• /
• 2022

Due to the characteristics of the railway system, a fleet consists of multiple railway vehicles, and a project contract is made by supplying multiple fleets to the customer. If the project fails to meet the due date, the manufacturer must compensate for the delay to the customer. In this paper, we analyze the operation strategies of the railway vehicle manufacturing factory using simulation, in which the layout adopts the concept of the flow lines, and when shortages of parts are considered. If there is a shortage of parts, the subsequent assembly process cannot proceed due to the nature of the assembly process. Thus, in order to overcome this problem, three strategies for performing assembly work are presented when the events of shortages are occurred. We also compare the strategies with respect to reduce the total cost which includes labor costs and compensation costs for delay.

• Journal of the Korean Society of Systems Engineering
• /
• v.16 no.2
• /
• pp.97-109
• /
• 2020

On March 11, 2011, an earthquake followed by a tsunami caused an extended station blackout (SBO) at the Fukushima Dai-ichi NPP Units. The accident was initiated by a total loss of both onsite and offsite electrical power resulting in the loss of the ultimate heat sink for several days, and a consequent core melt in some units where proper mitigation strategies could not be implemented in a timely fashion. To enhance the plant's coping capability, the Diverse and Flexible Strategies (FLEX) were proposed to append the Emergency Operation Procedures (EOPs) by relying on portable equipment as an additional line of defense. To assess the success window of FLEX strategies, all sources of uncertainties need to be considered, using a physics-based model or system code. This necessitates conducting a large number of simulations to reflect all potential variations in initial, boundary, and design conditions as well as thermophysical properties, empirical models, and scenario uncertainties. Alternatively, data-driven models may provide a fast tool to predict the success window of FLEX strategies given the underlying uncertainties. This paper explores the applicability of Artificial Intelligence (AI) to identify the success window of FLEX strategy for extended SBO. The developed model can be trained and validated using data produced by the lumped parameter thermal-hydraulic code, MARS-KS, as best estimate system code loosely coupled with Dakota for uncertainty quantification. A Systems Engineering (SE) approach is used to plan and manage the process of using AI to predict the success window of FLEX strategies under extended SBO conditions.

• Journal of the Korea Society for Simulation
• /
• v.8 no.4
• /
• pp.61-72
• /
• 1999

This paper presents an estimation method of container handling capacity and selection of resource allocation strategies of container terminals using the computer simulation models. Simulation models are developed to model container terminal consisting of 4 berths considering the berth allocation strategies, crane allocation strategies and the total number of container cranes using Arena simulation package. The proposed models do not consider the yard operations and gate operations. All the input parameters for the models are estimated on the basis of the existing container terminal operation data and the planning data for the automated container terminal planned by Korean government. Four berth allocation strategies and three crane allocation strategies are considered. The total number of container cranes considered ranges from 12 to 15. Non-terminating simulation techniques are utilized for the performance comparison among alternatives. The performance measures such as average ship turnaround time, average ship waiting time, average ship service time, the number of containers handled per year, and the number of ships processed per year are used. The result shows that the berth allocation strategy minimizing the sum of the number of ships waiting, the number of busy container cranes and number of ships handled performs better than any other berth allocation strategies. In addition, the crane allocation strategy allocating up to 5 container cranes per berth performs better than any other crane allocation strategies. Finally there are no significant performance differences among the alternatives consisting of different total number of container cranes allocated.

• East Asian mathematical journal
• /
• v.40 no.2
• /
• pp.183-207
• /
• 2024

This study is a case study that considered fractional senses and fraction operation abilities for 107 gifted students in elementary school classes. In order to find out the fractional sense, in the first question comparing the sizes of fractions 2/3 and 4/5, the students showed a variety of strategies, but the utilization rate of strategies excluding reduction to a common denominator did not exceed 50%. The second question can be solved by using the first question. It is a problem of finding two fractions by selecting four from six numbers 1, 3, 4, 5, 6, and 7 to create two fractions of which sum does not exceed 1. The percentage of correct answers to this question was about 27% (29 out of 107). Only 5 out of 29 students found answers using the first question, and the rest of the students sought answers through trial and error in various calculations. It shows that the item arrangement method from a deductive perspective has no significant effect on elementary school students. The percentage of correct answers was about 27% in the questions to find out the fraction operation ability-the question of drawing a 4/3 bar using a given 3/8-sized bar and 30.7% (23 out of 75) of the students who had wrong answers showed insufficient splitting operation. In addition, it has been shown that the operation of partitioning and iterating to form numerical senses and fractional concepts related to the fractions of the students has no significant impact.