• Atmosphere
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• v.25 no.4
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• pp.685-692
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• 2015

In this study, the effects of trees on flow and scalar dispersion in an urban street canyon were investigated using a computational fluid dynamics (CFD) model. For this, we implemented the drag terms of trees to the CFD model, and compared the CFD-simulated results to the wind-tunnel results. For comparison, we considered the same building configuration as the wind-tunnel experiment. The trees were located at the center of street canyon with the aspect ratio (defined as the ratio of the street width to the building height) of 1. First, the flow characteristics were analyzed in the tree-free and high-density tree cases and the results showed that the CFD model reproduced well the flow pattern of the wind-tunnel experiment and reflected the drag effect of trees in the street canyon. Then, the dispersion characteristics of scalar pollutants were investigated for the tree-free, low-density tree and medium-density tree cases. In the tree-free case, the nondimensionalized concentration distribution simulated by the CFD model was quite similar to that in the wind-tunnel experiment in magnitude and pattern. The correlation coefficients between the measured and simulated concentrations are more than 0.9 in all the cases. As the tree density increased, nondimensionalized concentration increased (decreased) near the wall of the upwind (downwind) building, which resulted from the decrease in wind speed case by the drag effect of trees. However, the CFD model underestimated (overestimated) the concentration near the wall of upwind (downwind) building.

• Spatial Information Research
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• v.19 no.6
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• pp.75-86
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• 2011

This paper proposes a modified way to delimit the boundary of Busan metropolitan area and compares the empirical analysis with the existing metropolitan area boundary. More specifically, the present state of the metropolitan transportation network is reflected by service area analysis in our study area. The analysis of the linkage between the central city and its fringes considers various travel behaviors as well as commuting to work and school, based on origin-destination trip information. In addition, more diverse indices are applied to the analysis of urban characteristics, and the land cover map is used as well. Compared with the current Busan metropolitan area boundary, our empirical analysis captures the status quo of the undergoing spatial dynamics such as the newly form ed homogeneous sphere of living in our study area.

• Particle and aerosol research
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• v.9 no.2
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• pp.79-87
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• 2013

In this study, the characteristics of turbulent flow and collection efficiency for an one-stage electrostatic precipitator(ESP) with slit type collecting electrode for urban railway underground tunnels were obtained using computational fluid dynamics(CFD) commercial code FLUENT 6.3 and lab-scale experiments. The electrostatic precipitator was operated under high gas velocity(3~12m/s). Five different designs of collecting electrode, flat plate-type and a slit-type of 3mm, 5mm, 7mm and 10mm slit width and four various gas velocity(3, 6, 9, and 12m/s) were used and applied. A standard k-${\varepsilon}$ model in CFD commercial code FLUENT 6.3 was used for flow simulation. The flow simulation results showed that the turbulent intensity of flat plate-type was higher than slit-type under all gas velocity conditions and also the turbulent intensity of flat plate-type was increased continuously, but in case of slit-type was maintained at constant range. And, the turbulent intensity was decreased according to increasing of slit width. The experimental results showed that the collection efficiency of slit-type was higher than flat plate-type under all gas velocity conditions. And, over 6m/s gas velocity condition, the collection efficiency of 5mm and 7mm was highest, when compared to 3mm and 10mm.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.12
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• pp.1559-1565
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• 2013

This study aims to investigate the dynamic interaction characteristics between Maglev vehicles and an elevated guideway. A more detailed model for the dynamic interaction of the vehicle/guideway is proposed. The proposed model incorporates a 3D full vehicle model based on prototyping, flexible guideway by a modal superposition method, and levitation electromagnets including the feedback controller into an integrated model. The proposed model was applied to an urban transit Maglev developed for a commercial application to analyze the dynamic response of the vehicle and guideway, and the effect of the surface roughness of the rail, mid-span guideway deflections, and air gap variations are then investigated from the numerical simulation.

• Smart Structures and Systems
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• v.23 no.6
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• pp.653-667
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• 2019

Using cross-ties to connect cables together when forming a cable network is regarded as an efficient method of mitigating cable vibrations. Cross-ties have been extended and fixed on bridge decks or towers in some engineering applications. However, the dynamics of this kind of system need to be further studied, and the effects of extending cross-links to bridge decks/towers on the modal response of the system should be assessed in detail. In this paper, a system of two cables connected by an inter-supported cross-link with another lower cross-link extended to the ground is proposed and analyzed. The characteristic equation of the system is derived, and some limiting solutions in closed form of the system are derived. Roots of cable system with special configurations are also discussed, attention being given to the case when the two cables are identical. A predictable mode behavior was found when the stiffness of inter-connection cross-link and the cross-link extended to the ground were the same. The vector of mode energy distribution and the degree of mode localization index are proposed so as to distinguish global and local modes. The change of mode behaviors is further discussed in the case when the two cables are not identical. Effects of cross-link stiffness, cross-link location, mass-tension ratio, cable length ratio and frequency ratio on $1^{st}$ mode frequency and mode shape are addressed.

• Ecology and Resilient Infrastructure
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• v.9 no.1
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• pp.77-82
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• 2022

This study aims to understand how mobile and stationary air pollution sources affect the air quality and soil properties in urban parks. We selected three sites of urban parks in Seoul as follows: Ha-neul Park in Mapo-gu (Site_M), Ill-won Eco-Park in Gangnam-gu (Site_G), and Yangjae Citizen's Forest in Seocho-gu (Site_Y), and compared the results of each site's traffic volume, air quality concentration, and soil analysis. Traffic volume was high in Site_M, followed by Site_G and Y; Site_M and G were closer to the resource recovery facility than Site_Y. Hence, we hypothesized that PM and NO₂ concentrations in the atmosphere were higher in Site_M than Site_G and Y, causing different soil nitrogen content among sites due to different atmospheric deposition. Consistent with our hypothesis, the concentrations of PM2.5 and NO₂ were higher in Site_M and G than Site_Y, while Site_Y had higher PM10 than other sites. The soil NO₃^- contents showed no significant difference among three sites, whereas the soil NH₄+ content was extremely high in Site_Y. This high content of soil NH₄⁺ is thought to be due to acidification from excessive fertilization. Lower soil pH of Site_Y further supported the evidence of heavy fertilization in this site. Overall nitrogen dynamics implies that soil nitrogen status is more influenced by park management such as fertilization rather than atmospheric deposition. Despite of lower soil NH₄⁺ content of Site_M and G than Y, vegetation vitality looked similar among three sites. This indirectly indicates that excessive fertilizer input in urban park management needs to be reconsidered. This study showed that even if the air quality was different due to mobile and stationary sources, it did not directly affect the soil nitrogen nutrient status of the adjacent urban park.

• Korean Journal of Social Welfare
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• v.57 no.2
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• pp.351-374
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• 2005

This study examines dynamics of poverty in Korea, focusing on poverty duration and its determinants. Data come from Korean Labor and Income Panel Study(KLIPS), 1998-2003. KLIPS is a longitudinal survey of 5,000 families and their members which are representative of urban residents in Korea. Respondents of KLIPS annually report detailed information on their income, economic activities, and other socio-economic characteristics. This study use poverty exit probabilities to generate distributions of spell lengths, following Bane and Ellwood(1986)'s methodology. This study finds a high level of poverty exit rates in Korea. About three quarters of those beginning a poverty spell exit from poverty within two years. Only 14.3 percent of all the poverty spells consist of long spells which persists five years or more. Yet, a different picture emerges when spells of the poor persons at a given time are analysed. Persistent poor occupy a considerable share of all the poor. Almost 50 percent of those who would be in poverty at a given time are in the midst of poverty spells lasting five years or more. When repeat spells of poverty are also included in the analyses, the proportion of long-term poor increases further. 63 percent of persons poor at a given time are long-termers. The majority of long-term poor are members of families headed by the aged. They show both a low level of poverty exit rates and a high level of reentry rates, and thus are most likely to experience long-term poverty. In the first place, they occupy a substantial share of all the poor. The second who are likely to be poor longer is members of families headed by non-aged women. Researchers have recentlty paid much attention to the working poor who have increased since the economic crisis in 1997. Yet, it is very likely that families headed by non-aged male who largely consist of the working poor temporarily experience poverty. Findings for this study suggest that further studies and policy proposals addressing persistent poverty are necessary.

• Journal of Korean Society of Transportation
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• v.13 no.2
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• pp.19-42
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• 1995

1980년대 후기부터 교통정책의 우선 목표는 지역경제성장 자체가 교통문제를 스스로 해결할 수 있도록 하기 위하여 종래의 관리 중시의 정책은 다시 토지이용 정책으로 변화를 초래하엿다. 오늘날 대도시는 개개 졍제활동 주체들의 동적인 경제 행태에근거하여 분산구조를 띠고 있다. 이러한 동적인 경제행태에 미치는 요소들은 교통체계와 토지이용과 상호연관성의 연구에 필수적인 지가, 인구분포, 통행행태등이다. 그러나 전통적인 단핵도시 모형은 대도시의 분산구조형태의 동적인 과정을 설명하는데는 한계가 있다. 본 연구는 대도시의 변천과정을-도심 및 부심의 출현·소멸현상-설명함으로써 도시교통정책 필수적인 입지와 통행패턴에 대한 새로운 동태적 이론의 기초를 제공하는데 그 목적이 있다. 이를 위하여 지역경제 성장과 도시공간구조와의 동태적관계를 통합하는 토지이용과 교통의 연속 모형을 개발·응용하였다. 개발된 모형에서는 교통량에 따른 교통비용, 도시공간구조로 인한 외부효과들, 경제활동주체들의 비동질성, 이주비용, 그리고 집적 이익등이 매기마다 내생적으로 결정되어 대도시의 공간구조 변화를 설명한다. 경제 호라동주체들간의 ? 호물리적 교류는 소득 증대에 의하여 경제구조가 변함에 따라 새로이 결정된다. 가상적 도시와 자료를 가지고 실험한 결과 비동질적인 경제주체들의 불균형적 성장이 장기적으로 도시구조에 영향을 미치며, 기본적인 경제행위에 따라 장기동태적인 과정을 통하여나타나는 도시의 분산구조형태의 중요성을 보여주고 있다. 또한 교통비용의 변화에 따른 민감도분석을 통하여 모형의 실용성을 검정하였다.

• International Journal of Automotive Technology
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• v.5 no.2
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• pp.77-88
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• 2004

Narrow commuter vehicles can address many congestion, parking and pollution issues associated with urban transportation. In making narrow vehicles safe, comfortable and acceptable to the public, active tilt control systems are likely to playa crucial role. This paper focuses on the development of an active direct tilt control system for a narrow vehicle that utilizes an actuator in the vehicle suspension. A simple PD controller can stabilize the tilt dynamics of the vehicle to any desired tilt angle. However, the challenges in the tilt control system design arise in determining the desired lean angle in real-time and in minimizing tilt actuator torque requirements. Minimizing torque requirements requires the tilting and turning of the vehicle to be synchronized as closely as possible. This paper explores two different control design approaches to meet these challenges. A Receding Horizon Controller (RHC) is first developed so as to systematically incorporate preview on road curvature and synchronize tilting with driver initiated turning. Second, a nonlinear control system that utilizes feedback linearization is developed and found to be effective in reducing torque. A close analysis of the complex feedback linearization controller provides insight into which terms are important for reducing actuator effort. This is used to reduce controller complexity and obtain a simple nonlinear controller that provides good performance.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.3
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• pp.1533-1556
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• 2017

The concept of trust in vehicular ad hoc networks (VANETs) is usually utilized to assess the trustworthiness of the received data as well as that of the sending entities. The quality of safety applications in VANETs largely depends on the trustworthiness of exchanged data. In this paper, we propose a self-organized distributed trust computing framework (DTCF) for VANETs to compute the trustworthiness of each vehicle, in order to filter out malicious nodes and recognize fully trusted nodes. The proposed framework is solely based on the investigation of the direct experience among vehicles without using any recommendation system. A tier-based dissemination technique for data messages is used to filter out non authentic messages and corresponding events before even going farther away from the source of the event. Extensive simulations are conducted using Omnet++/Sumo in order to investigate the efficiency of our framework and the consistency of the computed trust metrics in both urban and highway environments. Despite the high dynamics in such networks, our proposed DTCF is capable of detecting more than 85% of fully trusted vehicles, and filtering out virtually all malicious entities. The resulting average delay to detect malicious vehicles and fraudulent data is showed to be less than 1 second, and the computed trust metrics are shown to be highly consistent throughout the network.