• Geomechanics and Engineering
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• 제29권3호
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• pp.207-218
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• 2022

In submerged floating tunnels (SFTs), a next-generation maritime transportation infrastructure, the tunnel module floats in water due to buoyancy. For the effective and economical use of SFTs, connection with the ground is inevitable, but the stability of the shore connection is weak due to stress concentration caused by the displacement difference between the subsea bored tunnel and the SFT. The use of an elastic joint has been proposed as a solution to solve the stability problem, but it changes the dynamic characteristics of the SFT, such as natural frequency and mode shape. In this study, the finite element method (FEM) was used to simulate the elastic joints in shore connections, assuming that the ground is a hard rock without displacement. In addition, a small-scale model test was performed for FEM model validation. A parametric study was conducted on the resonance behavior such as the natural frequency change and velocity, stress, and reaction force distribution change of the SFT system by varying the joint stiffness under loading conditions of various frequencies and directions. The results indicated that the natural frequency of the SFT system increased as the stiffness of the elastic joint increased, and the risk of resonance was the highest in the low-frequency environment. Moreover, stress concentration was observed in both the SFT and the shore connection when resonance occurred in the vertical mode. The results of this study are expected to be utilized in the process of quantitative research such as designing elastic joints to prevent resonance in the future.

• 한국IT서비스학회지
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• 제10권4호
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• pp.243-258
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• 2011

With increasing interest in ubiquitous computing technology, an infrastructure for the short-distance wireless communication has been extended socially, bringing spotlight to the security system using the image or location. In case of existing security system, there have been issues such as the occurrences of blind spots, difficulty in recognizing multiple objects and storing of the unspecified objects. In order to solve this issue, zone-based location-estimation search system for the image have been suggested as an alternative based on the real-time location determination technology combined with image. This paper intends to suggest the search service for the image zone-based location-estimation. For this, it proposed the location determination algorism using IEEE 802.15.4/ZigBee's RSSI and for real-time image service, the RTP/RTCP protocol was applied. In order to combine the location and image, at the event of the entry of the specified target, the record of the time for image and the time of occurrence of the event on a global time standard, it has devised a time stamp, applying XML based meta data formation method based on the media's feature data based in connection with the location based data for the events of the object. Using the proposed meta data, the service mode which can search for the image from the point in time when the entry of the specified target was proposed.

• 한국정보통신학회논문지
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• 제13권4호
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• pp.759-764
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• 2009

본 논문에서는 IEEE 802.11 무선 랜의 인프라스트럭쳐 모드에서 성능을 향상시키기 위한 새로운 매체 접근 제어(MAC) 프로토콜을 제안한다. 각 단말은 beacon으로부터 전송되는 파라미터와 접속 연결 시에 AP로부터 부여받은 자신의 고유한 ID를 사용하여 단말들 내에서 유일한 백오프 값을 생성하여, 데이터 전송 시에 해당 백오프 값만큼의 유휴 슬롯을 보낸 후 데이터를 전송한다. 제안한 백오프 방식을 따를 경우 단말들 간의 충돌 없는 접속이 가능하며, 시뮬레이션을 통해 성능분석을 한 결과, 기존의 IEEE 802.11 프로토콜의 CSMA/CA 표준 방식과 비교해서 채널 이용률이 늘어나고 패킷 지연이 감소함을 볼 수 있었다.

• Journal of Communications and Networks
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• 제12권2호
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• pp.158-167
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• 2010

The energy efficiency of wireless infrastructure and terminals has been drawing renewed attention of late, due to their significant environmental cost. Emerging green communication paradigms such as cognitive radios, are also imposing the additional requirement of flexibility. This dual requirement of energy efficiency and flexibility poses new design challenges for implementing radio functional blocks. This paper focuses on the area vs. power trade-offs for the type of channel filters that are required in the digital frontend of a flexible, energy-efficient radio. In traditional CMOS circuits, increased area was traded for reduced dynamic power consumption. With leakage power emerging as the dominant mode of power consumption in nanoscale CMOS, these trade-offs must be revisited due to the strong correlation between area and leakage power. The current work discusses how the increased timing slacks obtained by increasing the parallelism can be exploited for overall power reduction even in nanoscale circuits. In this context the paper introduces the notion of 'area efficiency' and a metric for evaluating it. The proposed metric has also been used to compare the area efficiencies of different classes of time-shared filters.

• Geomechanics and Engineering
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• 제12권6호
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• pp.983-1001
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• 2017

The extent by which economy and safety concerns can be addressed in earth retaining structure design depends on the accuracy of the assumed failure surface. Accordingly, this study attempts to investigate and quantify mechanical backfill properties that control failure surface geometry of cohesionless backfills at the active state for translational mode of wall movements. For this purpose, a small scale 1 g physical model study was conducted. The experimental setup simulated the conditions of a backfill behind a laterally translating vertical retaining wall in plane strain conditions. To monitor the influence of dilative behavior on failure surface geometry, model tests were conducted on backfills with different densities corresponding to different dilation angles. Failure surface geometries were identified using particle image velocimetry (PIV) method. Friction and dilation angles of the backfill are calculated as functions of failure stress state and relative density of the backfill using a well-known empirical equation, making it possible to quantify the influence of dilation angle on failure surface geometry. As a result, an empirical equation is proposed to predict active failure surface geometry for cohesionless backfills based on peak dilatancy angle. It is shown that the failure surface geometries calculated using the proposed equation are in good agreement with the identified failure surfaces.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권3호
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• pp.1229-1248
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• 2016

With the feature of convenience and low cost, remote healthcare monitoring (RHM) has been extensively used in modern disease management to improve the quality of life. Due to the privacy of health data, it is of great importance to implement RHM based on a secure and dependable network. However, the network connectivity of existing RHM systems is unreliable in disaster area because of the unforeseeable damage to the communication infrastructure. To design a secure RHM system in disaster area, this paper presents a Secure VANET-Assisted Remote Healthcare Monitoring System (SVC) by utilizing the unique "store-carry-forward" transmission mode of vehicular ad hoc network (VANET). To improve the network performance, the VANET in SVC is designed to be a two-level network consisting of two kinds of vehicles. Specially, an innovative two-level key management model by mixing certificate-based cryptography and ID-based cryptography is customized to manage the trust of vehicles. In addition, the strong privacy of the health information including context privacy is taken into account in our scheme by combining searchable public-key encryption and broadcast techniques. Finally, comprehensive security and performance analysis demonstrate the scheme is secure and efficient.

• 한국강구조학회 논문집
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• 제26권2호
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• pp.69-79
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• 2014

본 연구에서는 콘크리트 섬유보강플라스틱(FRP)로 보강된 철골보의 정적 휨하중상태에서 휨거동에 관한 실험결과를 제시하였다. 아라미드섬유 스트립과 탄소섬유 스트립으로 보강된 4개의 실험체를 제작하였으며, 1개의 기준실험체를 제작하였다. 이중 두 실험체는 부분보강방식으로 보강되었다. H빔은 두 종류의 파괴모드를 가지고 있는데, (1) 부분보강 실험체에서는 FRP 스트립이 탈락(debonding)되는 파괴모드를 보이고 있으며, 전면보강 실험체에서는 FRP 스트립이 파단(rupture)되는 거동을 보이고 있다. 실험결과 16%의 휨내력 상승효과를 관찰하였다.

• 한국정보처리학회논문지
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• 제5권5호
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• pp.1140-1150
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• 1998

본 논문의 목적은 여러 다른 유형의 정보를 사용하고 다자간에 공동작업을 지원하는 응용의 요구사항을 분석하고, 이러한 특성을 갖는 응용이 필요로 하는 유용한 공통 서비스를 제공함으로 개발 환경을 지원하는 데 있다. 응용 계층의 수평 서비스로서 다자간 대화형 응용 서비스와 기반 구조 계층의 지원 서비스로서 다중 세션 관리 서비스가 정의되었으며, 개방형 분산 처리 시스템의 개념과 규칙에 따라 설계되었다. 따라서, 응용 개발자들은 이 두 서비스를 이용하여 본 논문에서 고려한 특성을 갖는 응용을 구축할 수 있을 것이다.

• 한국정보과학회논문지:컴퓨팅의 실제 및 레터
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• 제14권3호
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• pp.266-270
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• 2008

블루투스(Bluetooth)는 별도의 기반 인증 시설없이 각 디바이스간의 독립적인 인증과정을 통해 데이타를 서로 전송하는 기술을 사용하고 있다. 이러한 특징 때문에 이전에 기반 인중시설을 이용하는 네트워크에서는 발생하지 않았던 취약점들이 발생할 수 있으며, 가장 대표적인 문제가 위치 추적 공격이다. 따라서 본 논문에서는 디바이스 위치추적공격에 대해 살펴보고 그에 대한 해결책으로 익명모드를 제안한다. 제안된 방법은 발생 가능한 공격시나리오에 대해 분석하고 성능을 평가하였으며, 이를 통해, 기존 방법에 비해 수행 시간과 메모리 소비 측면에서 큰 차이를 보이지 않으면서도 위치 추적 공격에 대해 더 강인하게 동작함을 보였다.

• Computers and Concrete
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• 제26권1호
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• pp.11-20
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• 2020

Concrete are the most widely used manmade materials for infrastructure construction across the world. These constructions gradually aged and damaged due to long-term use. However, there does not exist an efficient concrete recycling method with low energy consumption. In this study, concrete was regarded as a heterogeneous material composed of coarse aggregate and cement mortar. And the failure mode of concrete under ultrasonic dynamic loading was investigated by finite element (FE) analysis. Simultaneously, a 3D random aggregate concrete model was programmed by APDL and imported into ABAQUS software, and the damage plastic constitutive model was applied to each phase to study the damage law of concrete under dynamic loading. Meanwhile, the dynamic damage process of concrete was numerically simulated, which observed ultrasonic propagating and the concrete crushing behavior. Finally, the FE simulation considering the influence of different aggregate volume and aggregate size was carried out to illustrate the damage level of concrete.