• Journal of Power System Engineering
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• v.14 no.5
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• pp.76-82
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• 2010

This paper investigates the optimum operating conditions to construct total automatic control system with high energy efficiency of a newly developed seawater ice machine. The machine has an electronic expansion valve(EEV) and a variable speed rotating drum with an evaporator installed inside. The coefficient of performance(COP) was used as an index to evaluate energy efficiency of the machine. At first, the opening angle of EEV was adjusted to obtain COP of the machine at a constant speed of the drum. Then, we checked seawater ice product versus opening angles of the EEV. Finally, effect of drum's rotating speed in response to product of seawater ice and seawater ice temperature were considered.

• Journal of the Korea Society for Simulation
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• v.12 no.2
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• pp.55-62
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• 2003

The explosive Increase of wireless networks and the advancement of mobile devices lead to the expansion of mobile environment. In accordance with the development of mobile environment, the need to use mobile database is increased sharply, and also it accompanies the related problems. The current mobile database system is based on the centralized method from which a synchronized server manages multiple mobile database management system to synchronize. From this mobile system architecture, several kinds of problems can be detected such as the management of synchronization issues between mobile databases and the transaction management issues. Furthermore, the current mobile database management system does not consider any solution on the fault tolerance. To solve those problems, this paper proposes the mobile agent-based mobile database management system. The proposed system provide high confidence and efficiency by enhancing the network efficiency and fault tolerance through the mobile grouping.

• Journal of Engineering Education Research
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• v.22 no.5
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• pp.3-12
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• 2019

Due to the expansion of rolling admissions and diversification of college admissions, the widening gap between the level of scholastic ability and academic performance is the reality of college education. Thus, based on the incoming class of College A, this study analyzes the correlation between incoming students who enrolled in a college mathematics course during their first semester. Through this analysis, this study searches for a way to efficiently instruct students from various learning backgrounds when enrolled in the same course. Also, this study searches for a solution to lower the deviation of college mathematics' academic performance among engineering majors by examining the efficiency of a joint managed college mathematics curriculum.

• International Journal of Computer Science & Network Security
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• v.22 no.1
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• pp.255-261
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• 2022

Routing Protocol for Low-Power and Lossy Networks (RPLs) in Internet of Things (IoT) is currently one of the most popular wireless technologies for sensor communication. RPLs are typically designed for specialized applications, such as monitoring or tracking, in either indoor or outdoor conditions, where battery capacity is a major concern. Several routing techniques have been proposed in recent years to address this issue. Nevertheless, the expansion of the network lifetime in consideration of the sensors' capacities remains an outstanding question. In this research, aANN-CUCKOO based optimization technique is applied to obtain a more efficient and dependable energy efficient solution in IOT-RPL. The proposed method uses time constraints to minimise the distance between source and sink with the objective of a low-cost path. By considering the mobility of the nodes, the technique outperformed with an efficiency of 98% compared with other methods. MATLAB software is used to simulate the proposed model.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.8
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• pp.3529-3550
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• 2016

In heterogeneous networks (HetNets), energy saving is vital for a sustainable network development. Many techniques, such as spectrum allocation, network planning, etc., are used to improve the network energy efficiency (EE). In this paper, micro BSs utilizing cell range expansion (CRE) and spectrum allocation are considered in multi-channel heterogeneous networks to improve EE. Hotspot region is assumed to be covered by micro BSs which can ensure that the hotspot capacity is greater than the average demand of hotspot users. The expressions of network energy efficiency are derived under shared, orthogonal and hybrid subchannel allocation schemes, respectively. Particle swarm optimization (PSO) algorithm is used to solve the optimal ratio of subchannel allocation in orthogonal and hybrid schemes. Based on the results of the optimal analysis, we propose three service control strategies on the basis of large-scale user behaviors, i.e., adjust micro cell rang expansion (AmCRE), adjust micro BSs density (AmBD) and adjust micro BSs transmit power (AmBTP). Both theoretical and simulation results show that using shared subchannel allocation scheme in AmBD strategies can obtain maximal EE with a very small area ratio. Using orthogonal subchannel allocation scheme in AmCRE strategies can obtain maximal EE when area ratio is larger. Using hybrid subchannel allocation scheme in AmCRE strategies can obtain maximal EE when area ratio is large enough. No matter which service control strategy is used, orthogonal spectrum scheme can obtain the maximal hotspot user rates.

• Journal of the Korea Institute of Building Construction
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• v.18 no.2
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• pp.117-123
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• 2018

The increase in energy efficiency has became a significantly important issue for building construction and maintenance. The energy efficiency is known to be achieved by using a material with lower thermal conductivity, and the best method is to increase the internal porosity of the material. Typical ways to increase internal porosity within cementitious composite are to use foaming agents or to use reactive powder such as aluminum. However, in this work, hydrogen peroxide was chosen as an alternative material to make lightweight cement mortar. The volume expansion of fresh cement mortar and unit weight, compressive strength and thermal conductivity of 28 day old cement mortar were measured. According to the experimental results, the incorporation of hydrogen peroxide increased internal porosity, and thereby reducing the compressive strength and thermal conductivities of cement mortar. It was found that hydrogen peroxide can be successfully used to produce lightweight mortar for thermal insulation purposes of buildings.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.4
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• pp.63-72
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• 2013

A Mach 5 nozzle and a diffuser of the Scramjet Engine Test Facility (SETF) were made for a hydrocarbon-fueled scramjet engine. SETF, attached with a diffuser guide, started with a model of 60% blockage, though the model engine could not start by over expansion of the facility nozzle. The model was moved into the nozzle to escape the shock generated from the nozzle exit, both SETF and the engine could start. The pitot rake experiments (blockage of 2.3%) were done for measuring the core flow in the test section. From the pitot experiments, the core flow was expanded by an under expansion. It means that the core flow in the test section was related with a model blockage. SETF and the engine with a blockage of 33% work normally. From a series of experiments, SETF started with a normal shock efficiency of 58%, regardless of a blockage ratio.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.44 no.3
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• pp.39-49
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• 2021

The Korean Air-Force aircraft maintenance depot paints the exterior of various aircraft, including high-tech fighters. Aircraft exterior painting is a maintenance process for long-term life management by preventing damage to the aircraft surface due to corrosion. The de-painting process is essential to ensure the quality of aircraft exterior paints. However, because the Korean Air-Force's de-painting process is currently done with sanding or Plastic Media Blasting (PMB) method, it is exposed to harmful dust and harmful compounds and consumes a lot of manpower. This study compares the de-painting process currently applied by the ROK Air-Force and the more improved process of the US Air Force, and performs economic analysis for the introduction of advanced equipment. It aims to provide information that can determine the optimal time to introduce new facilities through Cost-Volume-Profit (CVP) analysis. As a result of the analysis, it was confirmed that the sanding method had the most economical efficiency up to 2 units per year, the PMB method from 3 to 21 units, and the laser method from 22 units or more. In addition, in a situation where the amount of de-painting work is expected to increase significantly due to the increase in fighters in future, BEP analysis was conducted on the expansion of the existing PMB method and the introduction of a new laser method. As a result of the analysis, it was confirmed that it is more economical to introduce the laser method when the amount of work exceeds the PMB work capacity(18 units per year). The paper would helpful to improve the productivity and quality of the Korean Air Force Aircraft maintenance depot through timely changes of facilities in the workplace in preparation for expansion.

• Journal of Integrative Natural Science
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• v.16 no.4
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• pp.139-145
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• 2023

Due to changes in the distribution system and increased demand for renewable energy, interest in technology to increase the limit capacity of distributed energy grid connection using grid flexible resources is also increasing. Recently, the distribution system system is changing due to the increase in distributed power from renewable energy, and as a result, problems with the limited capacity of the distribution system, such as waiting for renewable energy to connect and increased overload, are occurring. According to the power generation facility status report provided by the Korea Power Exchange, of the total power generation capacity of 134,020 MW as of 2021, power generation capacity through new and renewable energy facilities is 24,855 MW, accounting for approximately 19%, and among them, power generation through solar power accounts for a total portion of the total. It was analyzed that the proportion of solar power generation facilities was high, accounting for 75%. In the future, the proportion of new and renewable energy power generation facilities is expected to increase, and accordingly, an efficient operation plan for the distribution system is needed. Advanced country-type NWAs that can integrate the operation and management of load characteristics for each line of the distribution system, power distribution, regional characteristics, and economic feasibility of distributed power in order to improve distribution network use efficiency without expanding distribution facilities due to the expansion of renewable energy. An integrated operating system is needed. In this study, in order to improve the efficiency of distribution network use without expanding distribution facilities due to the expansion of renewable energy, we developed a method that can integrate the operation and management of load characteristics for each line of the distribution system, power distribution, regional characteristics, and economic feasibility of distributed power. We want to develop an integrated operation system for NWAs similar to that of advanced countries.

• The Journal of Fisheries Business Administration
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• v.40 no.1
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• pp.1-26
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• 2009

The aquaculture management considers the maintenance of households lifehood more than profit maximization. As aquaculture industry has developed enterprise farms appeared, and the small and the large scale farms coexist. The features of coexistence could be summarized as followings. First of all, the large scale farms show the higher net profit while the small scale farms show the higher profit per 1ha and the earning rate. Secondly, in the case of over 2ha, the earning rate is stable in spite of the scale expansion. Moreover, in processing method, dried seaweed occupy the biggest proportion in the small scale farms while the raw seaweed occupy the biggest proportion in the large scale farms. Lastly, the scale of farms becomes larger, the participation rate of household labor rises. This thesis analyses the efficiency of Korean seaweed farms in the way of DEA model and suggests the improvements for the efficiency management. The mean technical, pure technical and scale efficiencies were measured to be 0.88, 0.96 and 0.91, respectively. Among the 20 farms included in the analysis, 10 were technically efficient and 12 were scale efficient. In conclusion, it is shown that the aquaculture farms has been becoming the form of coexistence. This appearance results in the effort for reducing the cost in the small scale farms and in profit maximization in the large scale farms. On the other hand, middle scale farms is inefficient compared with the small or large scale farms. Therefore, in order to achieve the efficiency, it is necessary to accomplish economy of scale by extending farm size or to cut expenses by reducing farm area. In other word, the efforts for achieving the efficiency is required in a different direction in spite of the same scale.