• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.7
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• pp.704-712
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• 2016

Recently, the installation of photovoltaic (PV) systems has been increasing due to the worldwide interest in eco-friendly and infinitely abundant solar energy. However, the output power of PV systems is highly influenced by the surrounding environment. For instance, a string of PV systems composed of modules in series may become inoperable under cloudy conditions or when in the shade of a building. In other words, under these conditions, the existing control method of PV systems does not allow the string to be operated in the normal way, because its output voltage is lower than the operating range of the grid connected inverter. In order to overcome this problem, we propose a new control method using a DC-DC voltage regulator which can compensate for the voltage of each string in the PV system. Also, based on the PSIM S/W, we model the DC-DC voltage regulator with constant voltage control & MPPT (Maximum Power Point Tracking) control functions and 3-Phase grid connected inverter with PLL (Phase-Locked Loop) control function. From the simulation results, it is confirmed that the present control method can improve the operating efficiency of PV systems by compensating for the fluctuation of the voltage of the strings caused by the surrounding conditions.

• Journal of the Korean Institute of Landscape Architecture
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• v.25 no.3
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• pp.12-24
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• 1997

One argument of this study is that the policy to handle and landscape of cultural and historical property had to do with people's visual preferences. This study seeks to investigate people's visual preferences toward the landscape of cultural /historical property, specifically dealing with 'Namdaemun', which is the first class cultural property of Korea. People's visual preference was specifically examined into the four specific concepts : 'visual identity','harmony','beauty of the target property', and 'overall beauty'. Two objective variables, such as, 'distance' between the viewer and the cultural property, and 'height' of background buildings were considered possible predictors of the four visual preference variables. Photos of 'Namdaemun' were taken at three different directions and at three different distances. The photographed images of 'Namdaemun' were transferred ito the digitalized graphic images, where the height of background buildings was artificially changed and simulated. The simulated visual images were taken into the slides again. A total of 59 students of the Department of Landscape architecture at Seoul City University were sampled as subjects. A series of 17 slides were shown to the subjects four times. The subjects were asked to check their preference ratings concerning the four concepts on a 7-point Likert scale. The results found in this study were as follows : 1) In the results of ANOVA, it was clear that people visually preferred the view where the height of background buildings were lower than 15 floors to the view of more than 15 floors . 2) From the results of the path analysis, it was found that 'harmony','visual identity' and 'beauty of the target property' were direct predictors of 'the overall beauty'. The 'height ' of background buildings and the viewer's 'distance' were not found to be direct predictors, however, they demonstrated their effects on 'the overall beauty' through the other variable, which were direct predictors of 'the overall beauty'. In sum, the longer the distance and the higher the background buildings, the lower people's preference with the 'overall beauty'. These indirect paths, in turn, also explain why and how the 'height' of background buildings and the viewer's 'distance' negatively influence the 'overall beauty'. An implication from the these results is that when the height of background buildings were not controllable, there would be some other strategies for improving people's visual preference toward the historical /cultural view. To increase 'visual identity' of the cultural property, for example, changing colors of the cultural property or increasing the lighting level, etc., would be one strategy, since the increased 'visual identity' will, in turn, increase 'the overall beauty'.

• Korean Journal of Construction Engineering and Management
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• v.18 no.4
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• pp.3-16
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• 2017

Forecasting cash flow is very important but is difficult and complicated to analysis in high-rise development projects. And An expected value which was forecasted on the early stage is likely to fluctuate due to uncertainties around such complicated huge project to consider the probable uncertainty. There are not objectified method which are able to cope with uncertainty of project, and feasibility study based on selected financial analysis does not include liquidity of cash flow. Through such a stochastic method, developer can cope with cash flow fluctuation and set up a financial plan. Also this study is meaningful for laying the foundation for high-rise development project and feasibility study as well as the suitability and accuracy of feasibility study. Analysis showed that NPV and IRR include residential apartments shows surplus revenue as return of apartments offset deficit of hotel and office. Factors influencing the project feasibility for high-rise development project are sales account of $1^{st}$ year and annual vacancy rate of office.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.4
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• pp.419-428
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• 2020

The flow past a wall mounted square cylinder, a typical and basic shape of building, bridge or offshore structure, was simulated using URANS computation through adoption of three turbulence models, namely, the k-ε model, k-ω model, and the v²-f model. It is well known that this flow is naturally unstable due to the Karman vortex shedding and exhibits a complex flow structure in the wake region. The mean flow field including velocity profiles and the dominant frequency of flow oscillation that was from the simulations discussed earlier were compared with the experimental data observed by Wang et al. (2004; 2006). Based on these comparisons it was found that the v²-f model is most accurate for the URANS simulation; moreover, the k-ω model is also acceptable. However, the k-ε model was found to be unsuitable in this case. Therefore, v²-f model is proved to be an excellent choice for the analysis of flow with massive separation. Therefore, it is expected to be used in future by studies aiming to control the flow separation.

• The Journal of the Acoustical Society of Korea
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• v.22 no.2
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• pp.121-128
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• 2003

Acoustic Echo Cancellation(m) is very active research topic having many applications like teleconference and hands-free communication and it employs Double Talk Detector(DTD) to indicate whether the near-end speaker is active or not. However. the DTD is very sensitive to the variation of acoustical environment and it sometimes provides wrong information about the near-end speaker. In this paper, we are focusing on the development of robust DTD algorithm which is a basic building block for reliable AEC system. The proposed AEC system consists of delayless subband AEC and narrow-band DTD. Delayless subband AEC has proven to have excellent performance of echo cancellation with a low complexity and high convergence speed. In addition, it solves the signal delay problem in the existing subband AEC. On the other hand, the proposed narrowband DTD is operating on low frequency subband. It can take most advantages from the narrow subband such as a low computational complexity due to the down-sampling and the reliable DTD decision making procedure because of the low-frequency nature of the subband signal. From the simulation results of the proposed narrowband DTD and wideband DTD, we confirm that the proposed DTD outperforms the wideband DTD in a sense of removing possible false decision making about the near-end speaker activity.

• Journal of the Korean Association of Geographic Information Studies
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• v.19 no.1
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• pp.180-196
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• 2016

To minimize the damage from disasters, various aspects of prevention, preparation, and response, etc. are being managed. Even though prevention and preparation are well conducted, irresistible calamities such as natural disasters may cause unexpected damage. Therefore, a system that can share the identical disaster information based on prompt disaster management and prediction must be developed and constructed for integrated disaster management. Especially, for a prompt disaster response, the same information needs to be shared between the related organization and the disaster prevention personnel such as on-site officials. Recent disaster management systems use high-capacity geographic information or other various factors for accurate disaster predictions. In case of using a recently constructed or researched 3D GIS, the system may not be used in some cases due to conflicts with hardware, etc. Thus, even though response information is secured using prediction simulation in advance, it is essentially difficult in some cases to share the common information when the system cannot be utilized or the extension of the corresponding data cannot be read. Therefore, this study aims to construct a system for dealing with disasters that shares the same prompt and accurate information in compliance with common data formats. The system is expected to reduce the existing disaster response time and minimize human and physical damage by assisting decision making through prompt responses.

• Journal of Korean Society of Steel Construction
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• v.24 no.3
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• pp.325-336
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• 2012

Smart base isolation systems developed for structures in high seismic regions cannot be directly applied to structures in regions of low-to-moderate seismicity, such as Korea. Therefore, the problems that occur by applying the smart base isolation system for high seismic regions to the structures in regions of low-to-moderate seismicity have been investigated in this study. To this end, a five-story building is used as an example, and an MR damper and low damping elastomeric bearings were used to compose a smart base isolation system. Artificial earthquakes are simulated for ground motions in regions of high and low-to-moderate seismicity. Based on numerical simulation results, the MR damper capacity that can provide good control is quite different among regions of high and low-to-moderate seismicity. Moreover, it is noted that the properties of a smart base isolation system for the regions of low-to-moderate seismicity should be carefully designed because the base isolation effects of the smart base isolation system for high seismic regions deteriorate when it is applied to the structures in regions of low-to-moderate seismicity.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.2
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• pp.135-146
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• 2020

To define an interface in a conventional level-set method, an analytical function must be revealed for an interfacial geometry. However, it is not always possible to define a functional form of level sets when interfaces become complex in a Cartesian coordinate system. To overcome this difficulty, we have developed a new level-set formalism that discriminates the interior from the exterior of a CAD modeled interface by parameterizing the stereolithography (STL) file format. The work outlined here confirms the accuracy and scalability of the hydrodynamic reactive solver that utilizes the new level set concept through a series of tests. In particular, the complex interaction between shock and geometrical confinements towards deflagration-to-detonation transition is numerically investigated. Also, a process of flame spreading and damages caused by point source detonation in a real-sized plant facility have been simulated to confirm the validity of the new method built for reactive hydrodynamic simulation in any complex three-dimensional geometries.

• Journal of the Korean Institute of Intelligent Systems
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• v.20 no.1
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• pp.81-87
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• 2010

The coverage ability is one of essential techniques for the Robotic Vacuum Cleaner (RVC). Most of the RVCs rely on random or regular pattern movement to cover a target space due to the technical difficulties to implement localization and map and constraints of hardwares such as controller and sensors. In this paper, we consider two main issues which are low computational load and using sensors with very limited sensing capabilities. First, in our approach, computing procedures to build map and detect the RVC's position are minimized by simplifying data obtained from sensors. To reduce computational load, it needs simply presenting an environment with objects of various shapes. Another isuue mentioned above is regarded as one of the most important problems in our approach, because we consider that many RVCs use low-cost sensor systems such as an infrared sensor or ultrasonic sensor with limited capabilities in limited range, detection uncertainty, measurement noise, etc. Methods presented in this paper are able to apply to general RVCs equipped with these sensors. By both simulation and real experiment, we evaluate our method and verify that the proposed method guarantees a complete coverage.

• The Journal of the Acoustical Society of Korea
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• v.37 no.5
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• pp.369-377
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• 2018

This study investigated the effect of noise and reverberation on subjective measure of speech transmission performance for elderly person with hearing loss in residential space through listening test. Floor impact, road traffic, airborne, and drainage noise were employed as the residential noise, and several impulse responses were obtained through room acoustical computer simulation for an apartment building. Sound sources for the listening test consisted of residential noises and speech sounds for boh the young (the original sound) and the aged (the sound filtered out by filters with frequency responses of hearing loss of 65 years elderly person). In the listening test, subjects evaluated speech intelligibility and listening difficulty for the presented word ($L_{Aeq}$ 55 dB) at three noise levels ($L_{Aeq}$ 30, 40, 50 dB) and three reverberation times (0.5, 1.0, 1.5 s). Results showed that the residential space with noise level lower than equal to 50 dB ($L_{i,Fmax,AW}$) for jumping noise and 40 dB ($L_{Aeq}$) for road traffic, airborne, and drainage noise had speech intelligibility of 90 % and over and listening difficulty of 30 % and below. Speech intelligibility and listening difficulty for the aged sound source was shown to be 0 % ~ 5 % lower and 2 % ~ 20 % higher than those for the young sound source, respectively.