• Proceedings of the Korean Geotechical Society Conference
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• 2000.03b
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• pp.93-100
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• 2000

In this study, we used photoelastic coating method which is a kind of model test for examining the stress condition of rock masses around underground structures. Using this method, we could know adaptability and usefulness of photoelastic coating method for various shape of tunnel models. And, in spite of higher cross section efficiency, square shape model showed unstable status because of high stress concentration. So, we cut the slits at the each corner of tunnel, and we could make more stable stress condition by means of moving high stress concentration to rock mass.

• Journal of Korea Water Resources Association
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• v.44 no.5
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• pp.363-376
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• 2011

1-D hydrodynamic numerical models have been most widely used in the field of flood analysis. The model's input data are upstream/downstream boundaries, roughness coefficients, cross-sections, and so on, and computational distance step and time step are the most important factors in order to guarantee the computational accuracy, stability, and efficiency. In this study, a theoretical explanation is presented for the basis of the previous empirical selection criteria of cross-section's location; also, the estimation technique of computationally variable distance step is proposed to reflect the properties of flow at every computational time step. Combining this technique with 1-D unsteady numerical model, it was applied to two events of Teton dam failure flood and the Han River flood. The numerical experimental results demonstrate that the accuracy and stability is increased when used more interpolated cross-sections and show that the proposed technique of computationally variable distance step has the same order of accuracy with smaller numbers of cross-section than previous empirical selection criteria. The practical use of this technique will be possible to analyze the river floods with high efficiency as well as accuracy and stability.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.1085-1088
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• 2001

The process of styrofoam pattern that has been used for material of press die pattern depends chiefly on handwork. Laser manufacturing system developed to increase precision and efficiency of process that is also able to convert the design easily. Applying the RP(rapid prototyping) concept reversely, the unnecessary part of section is vapored away by heat source of laser beam after converting 3-D CAD model into cross-sectional shape information. Laser beam is line-scanned in plane specimens to measure the depth and width of cut, surface roughness, cross-sectional shape as converting laser power, scanning speed, cutting gas pressure. With these basic data, plane surface, inclined surface, hole, outer contour trimming process is experimented and optimum condition are obtained. In plane and inclined surface experiments, 15W laser power and 50mm/s scanning speed make superior processing property and 30W, 10mm/s make processing efficiency increase in trimming process. With these results, simple patterns were manufactured and the possibility of applying laser manufacturing system to styrofoam pattern was convinced.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.4 no.6
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• pp.1098-1115
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• 2010

An inseparable challenge associated with every random access network is the design of an efficient Collision Resolution Algorithm (CRA), since collisions cannot be completely avoided in such network. To maximize the collision resolution efficiency of a popular CRA, namely Binary Exponential Backoff (BEB), we propose a reactive backoff algorithm. The proposed backoff algorithm is reactive in the sense that it updates the contention window based on the previously selected backoff value in the failed contention stage to avoid a typical type of collision, referred as cross-collision. Cross-collision would occur if the contention slot pointed by the currently selected backoff value appeared to be present in the overlapped portion of the adjacent (the previous and the current) windows. The proposed reactive algorithm contributes to significant performance improvements in the network since it offers a supplementary feature of Cross Collision Exclusion (XCE) and also retains the legacy collision mitigation features. We formulate a Markovian model to emulate the characteristics of the proposed algorithm. Based on the solution of the model, we then estimate the throughput and delay performances of WLAN following the signaling mechanisms of the Distributed Coordination Function (DCF) considering IEEE 802.11b system parameters. We validate the accuracy of the analytical performance estimation framework by comparing the analytically obtained results with the results that we obtain from the simulation experiments performed in ns-2. Through the rigorous analysis, based on the validated model, we show that the proposed reactive cross collision exclusionary backoff algorithm significantly enhances the throughput and reduces the average packet delay in the network.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.5
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• pp.589-601
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• 1997

A computer simulation program of a high efficiency condensing heat exchanger is developed. The flue gas flows outside bare tube bundles both in strong cross flow and in weak counter flow and the cooling water inside the tubes. Condensing heat exchangers achieve high efficiency by reducing flue-gas temperatures to a level at which most of the water vapor in the flue gas is condensed and the latent heat associated with phase change of the water is recovered. The computer model has been verified by comparison with measured data. To verify the model, heat transfer coefficient was adjusted, along with the mass transfer diffusion coefficient and pressure drop coefficient, to achieve agreement between predicted and measured data. The efficiencies of heat exchanger increase 2.3 ~ 8.1% by condensations of 6.3 ~ 62.6% of the water vapor in the flue gas.

• 한국가시화정보학회:학술대회논문집
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• 2006.12a
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• pp.131-134
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• 2006

Whole flow fields of a room air conditioner (RAC) have been visualized by a Particle Image Velocimetry (PIV) technique to analyze the flow structure by various inlet and outlet angles, and to control an eccentric vortex which affects an efficiency and noise of the RAC. A test model with 5 stages of a cross flow fan has been manufactured and a transparent acryl has been installed at the side of the test model for the PIV experiment. The inlet and outlet flows and the flow inside the cross flow fan have been analyzed by varying the inlet grill angles and outlet blade angles. The movement of the eccentric vortex has been investigated experimentally by developing the measurement technique for the inner flow field of the cross flow fan, and the relationship between the control of the eccentric vortex and the inlet and outlet angles has been confirmed in this study.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.16 no.6
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• pp.1849-1876
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• 2022

Wireless Sensor Network (WSN) is considered as an integral part of the Internet of Things (IoT) for collecting real-time data from the site having many applications in industry 4.0 and smart cities. The task of nodes is to sense the environment and send the relevant information over the internet. Though this task seems very straightforward but it is vulnerable to certain issues like energy consumption, delay, throughput, etc. To efficiently address these issues, this work develops a cross-layer model for the optimization between MAC and the Network layer of the OSI model for WSN. A high value of duty cycle for nodes is selected to control the delay and further enhances data transmission reliability. A node measurement prediction system based on the Kalman filter has been introduced, which uses the constraint based on covariance value to decide the scheduling scheme of the nodes. The concept of duty cycle for node scheduling is employed with a greedy data forwarding scheme. The proposed Duty Cycle-based Greedy Routing (DCGR) scheme aims to minimize the hop count, thereby mitigating the energy consumption rate. The proposed algorithm is tested using a real-world wastewater treatment dataset. The proposed method marks an 87.5% increase in the energy efficiency and reduction in the network latency by 61% when validated with other similar pre-existing schemes.

• Journal of Ocean Engineering and Technology
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• v.29 no.4
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• pp.317-321
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• 2015

Many kinds of generation systems have been developed to use ocean energy. Among these, with the use of an oscillating water column (OWC) for power generation is attracting attention. The OWC-type wave power generation system converts wave energy into electricity by operating a generator turbine with the oscillating water level in a column of water. There are two ways to convert wave power into electricity using an OWC. One uses a cross-flow turbine using the water level inside the OWC. The other method uses the flow of air in a Wells turbine, which depends on the water level. An experiment was carried out using a 2-D wave tank in order to minimize the number of empirical tests. The design factors were taken from Koo et al. (2012) and the experimental environment assumed by free surface motion. This paper deals with characteristics of two types of wave energy conversion systems combine with a breakwater. One model uses an air-driven Wells turbine and a cross-flow water turbine. The other type uses a cross-flow water turbine. Wave energy converters with OWCs have mostly been studied using air-driven Wells turbines. The efficiency of the cross-flow turbine was about 15% higher than that of the other model, and the water level of the OWC internal chamber for the cross-flow water turbine and air-driven Wells turbine was less than about 40% lower than the one using only the cross-flow water turbine.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.2
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• pp.112-122
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• 2016

In line with the increase in consumer demand for mobile games, game companies face stiff competition. For a more successful marketing strategy, many game companies actively adopt Cross Promotion. The Cross Promotion marketing strategy in the mobile game is regarded as a low cost and high efficiency marketing method because the game companies provide new experiences to game users by utilizing existing game infrastructure and absorbing current users of game companies. Despite the advantages of Cross Promotion, there has been little practical study on the relationship between Cross Promotion and mobile game acceptance. Accordingly, the aim of this study was to determine the influential factors of Cross Promotion on the acceptance of mobile games. After reviewing previous research, a structural model was established, a survey was performed and the model was analyzed. The managerial implications are suggested along with the concluding remarks.

• Journal of Korea Port Economic Association
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• v.31 no.4
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• pp.39-52
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• 2015

The purpose of this paper is to empirically examine whether there are significant relations among rankings of cross-efficiency, web accessibility, and website evaluation. For this purpose, the study uses the KWAH-4 method developed by the Web Accessibility Laboratory in Korea, website evaluation method developed by the Business Development Bank of Canada (BDC), and the cross-efficiency model for 13 Asian container seaports including Korean, Chinese, and Japanese main ports in 3 years (2009, 2010, and 2013) using data for two cases: three inputs (depth, total area, and number of crane) and one output (TEU) in the first case and three inputs and two outputs (TEU and BDC overall score) in the second case. The main empirical results are as follows. First, the ranking orders of cross-efficiency, web accessibility, and website evaluation overall scores are not significantly correlated with each other. Second, if the BDC overall score is included in the output element, the correlation results are improved. However, the correlation coefficient is still low. The container port policy planners should introduce and consider the web accessibility and website evaluation scores when evaluating an efficiency-increasing plan for Korea's main container ports.