• Journal of Korean Society of Coastal and Ocean Engineers
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• v.23 no.4
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• pp.276-284
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• 2011

The rip current occurred at Haeundae beach was numerically investigated under directional random wave environment. The numerical simulation was performed using a fully nonlinear Boussinesq equation model, FUNWAVE which is capable of simulating nearshore circulation since it includes the effect of wave-induced momentum flux and horizontal turbulent mixing. The results of numerical simulation show the time-dependent evolution of the wave-induced nearshore circulation system (including rip current) that are caused by nonlinear transformation of directional irregular waves due to unique topography of Haeundae. From the results, it was found that rip current is well generated and developed where relatively lower wave height and relatively deeper water depth along the longshore direction, and sudden and strong events of rip current were observed.

• The Journal of the Acoustical Society of Korea
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• v.34 no.2
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• pp.98-107
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• 2015

It is investigated that there exists the possibility of the false target signals induced by reverberation in an active sonar system due to the internal waves in shallow water. The rays down-refracted from the internal waves may generate strong bottom-reverberation signals, which can result in false target signals. Sound waves emitted from a source propagate 3-dimensionally. Therefore, the study of internal waves on the reverberation should be studied for azimuthal direction as well as 2-dimensional (r-z) plane. Internal-wave modelling was conducted, based on solitons which were predicted with the various conditions such as, the range of source-soliton, horizontal widths of soliton. Variable depth sonar (VDS) was assumed as a source, of which the depth was located in the minimum sound speed layer in a simulation environment. Finally, the simulation on the reverberation level with time was made based on ray-based reverberation model, and the results implied that several false-target signals could be displayed on the PPI(Plan Position Indicator) scope simultaneously with range from source to soliton, and the horizontal width of soliton.

• Informatization Policy
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• v.17 no.3
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• pp.74-97
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• 2010

This paper investigates factors that have facilitated the rapid diffusion of broadband in South Korea. It finds that the quick spread of broadband access in South Korea is the result of combining the government's strategic ICT policy considering cultural traits, businesses'competitive efforts, and the timely explosion of domestic demand for IT service. This paper also discusses the impact of broadband diffusion on the digital divide. It finds that although there are still regional and age gaps in broadband access, the Korean government and businesses are working to alleviate these problems through various ways from systemic to physical ones. While the deployment of broadband cannot eliminate every issue of the digital divide, broadband access minimizes the digital divide by lowering the barrier to inequitable access to information. This paper concludes with a number of recommendations that address selected policy issues related to the spread of broadband Internet for its successful implementation.

• Magazine of the Korea Concrete Institute
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• v.7 no.5
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• pp.172-178
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• 1995

Concrete contains numerous microcracks at initially poured. The growth and propagation of nicrockacsk are believed tc finally incur the faiure of concrete. These processings are understood as a damage. Damage IS represented as a second-order tensor and crack is treated as a con tinuum phenomenon. In this paper, damage is characterized through the effective stress concept together with the hypothesis of elastic energy equivalence, and damage evolution law and constitutive equation of a damage model are derived by using the Helmholtz frte eriergy and the dissipation potential by means of the thermodynamic principles. The constitutive equation of the model includes the effects of elasticity, anisotropic damage and plasticity of concrete. There are two effective tangent stiffness tensors in this model : one is for elastic-darnage and the other for plastic damage. For the verification of the model, finite element analysis was performed for the analysis of concrete subjec:t to uniaxial and biaxial loading and the results obtained were compared with test results.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.14 no.3
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• pp.280-292
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• 1989

In this paper, the error rate equations of digitally modulated signals transmitted through the channel which is not only Gaussian/Impulsive noise but also multi-path fading have been derived. Using the derived equations for the error probabilities of ASK, QAM, CPSK, DPSK, FSK, and MSK signals, the error rate performances of digital modulation systems have been evaluated and represented in the graphs as the functions of CNR, Impulsive indes, the ratio of Gaussian noise power component to Impulsive noise power component, and fading figures. The results show that, in the deep fading environment, the error is occurred more frequency by Gaussian noise than Impulsive noise. And the comparison of various systems certifies that PSK is superior to the ohter systems in the deep fading or shallow fading environment.

• Journal of Energy Engineering
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• v.8 no.4
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• pp.540-545
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• 1999

The classical Fourier heat conduction equation is invalid at temperatures near absolute zero or at very early times in highly transient heat transfer processes. In such situations, a hyperbolic equation model for heat conduction based on the modified Fourier law is introduced because the wave nature of heat propagation becomes dominant. The Fourier model and the hyperbolic model for heat conduction are analyzed by using the Green's function technique together with the integral transform. Analytical expressions for the heat flux and temperature distributions in a finite slab subjected to a periodic surface heating at one of its surfaces are presented and the results obtained from each model are compared with each other. The thermal wave implied b the hyperbolic model is shown to travel through a medium and to reflect back toward the origin at the other insulated surface. On the other hand, the heat by the Fourier model propagates at an infinite speed instantaneously after a thermal disturbance is felt throughout the medium.

• Journal of Convergence for Information Technology
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• v.11 no.10
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• pp.138-143
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• 2021

As of this moment, we are tracing people who are closed contact with Covid-19 patients and trying to block the spread of Covid-19 through diagnostic tests. However, the incubation period of the confirmed case is two weeks, and it takes a lot of human resources, time, and money to trace the routes of the confirmed case. In particular, as the number of confirmed cases have been increasing, the cost for finding closed contacts and blocking them in advance exponentially have almost reached the limitation of the budget. In finding closed contacts, all citizens must record an electronic access list every time they visit an amenities such as a store or a restaurant. This is likely the invasion of the privacy of personal location information. In this study, we designed a system that keeps one's location in real time, it will download the movement information of the confirmed case which is collected by KDCA, and it will notify the user when there is an overlap. Moreover, then guide for diagnostic test in advance will be used. The proposed method can solve the difficulty of recording in an electronic access list when visiting a store, and it can block infringement of privacy without providing personal information from KDCA.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.2A
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• pp.289-295
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• 2008

The purpose of this study was to examine the flexural behavior of reinforced concrete beams strengthened with CFRP strips. A total of 12 rectangular beams were tested. Test variables in this study were the shapes, bonded length and the number of longitudinal layers of CFRP strips. From the experimental study, flexural capacity of the beams strengthened with CFRP strips significantly increased compared to the reinforced concrete beam without a CFRP strip. Maximum increase of ultimate strength was found about 120% more than the control beam. In this test, most of the strengthened beams failed suddenly due to the debonding of CFRP strips. It is also observed that the debonding of the strip was initiated in the flexural zone of the beam and propagated rapidly to the end of the beam. The ultimate tensile strains of CFRP strips in this test were occurred at the level of 36% of rupture tensile strength of the CFRP strip, and an analytical approach to compute the flexural strength of reinforced beams strengthened with CFRP strips based on the effective stresses was conducted.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.398-398
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• 2022

최근 수돗물 공급과정에 있어 적수, 유충 발생 등 지역 단위의 수질문제로 국민의 직간접적인 피해가 발생된 바 있다. 수질문제 발생 시, 소셜네트워크서비스(SNS)에 게시되는 피해 관련 의견은 시공간적으로 빠르게 확산되며, 궁극적으로는 물공급과정 전체의 부정적 인식증가와 신뢰도 저하를 초래한다. 따라서, 물공급시스템에서의 수질사고 발생을 빠르게 인지하는 다양한 방법론의 적용을 통한 피해 최소화를 위한 노력이 반드시 필요하다. 일반적으로 수질사고는 다양한 항목의 실시간 계측기에서 획득되는 시계열자료의 변화양상을 통해 판단할 수 있으나, 이와 같은 방법론의 효율적 적용을 위해서는 선진계측인프라의 도입이 선행되어야 한다. 본 연구에서는 국내의 발달된 정보통신기술환경을 활용하여, 물공급네트워크 내 수질사고인지를 위한 SNS 별 웹크롤링 방법론을 제안하고, 적용결과를 분석하였다. 방법론의 구현에 앞서, 각종 SNS 별(트위터, 인스타그램, 블로그, 네이버 카페 등) 프로그래밍을 통한 웹크롤링 가능여부, 정보획득 기간 등을 확인하였으며, 과거 유사 수질사고 발생 시 영향력과 관련 게시글이 크게 나타난 네이버 카페와 트위터를 중심으로 웹 크롤링 절차를 제시하였다. 네이버 카페의 경우 대상급수구역 내의 시민들이 다수 참여하는 카페를 목록화하고, 지자체명과 핵심 키워드(수돗물, 유충, 적수) 조합을 활용한 웹크롤링을 수행하여, 관련 게시물 건수와 의미를 실시간으로 분석하는 절차를 마련하였다. 개발된 SNS 별 웹크롤링 방법론에 따라 과거 수질사고가 발생된 바 있는 2개 이상의 지자체에 대한 분석을 실시하였으며, SNS 별 결과에 있어 차이점을 확인하여 제시하였다. 향후 제안된 방법을 적용하여 시공간적 수질사고 정보의 전파 및 확산양상을 추가적으로 분석할수 있을 것으로 기대된다.

• The Journal of the Acoustical Society of Korea
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• v.28 no.3
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• pp.260-267
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• 2009

It is very difficult to form a desired complex sound field at a designated region precisely as an application of acoustic arrays, which is one of important objects of array systems. To solve the problem, a filter design method was suggested, which employed the concept of an inverse method using the acoustical holography based on the boundary element method. In the acoustical holography used for the source identification, the measured field data are employed to reconstruct the vibro-acoustic parameters on the source surface. In the analogous problem of source array design, the desired field data at some specific points in the sound field was set as constraints and the volume velocity at the surface points of the source plane became the source signal to satisfy the desired sound field. In the filter design, the constraints for the desired sound field are set, first. The array source and given space are modelled by the boundary elements. Then, the desired source parameters are inversely calculated in a way similar to the holographic source identification method. As a test example, a target field comprised of a quiet region and a plane wave propagation region was simultaneously realized by using the array with 16 loudspeakers.