• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.2
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• pp.138-149
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• 2000

Various modeling techniques for ultrasonic wave propagation and scattering problems in finite solid media are presented. Elastodynamic boundary value problems in inhomogeneous multi-layered plate-like structures are set up for modal analysis of guided wave propagation and numerically solved to obtain dispersion curves which show propagation characteristics of guided waves. As a powerful modeling tool to overcome such numerical difficulties in wave scattering problems as the geometrical complexity and mode conversion, the Boundary Element Method(BEM) is introduced and is combined with the normal mode expansion technique to develop the hybrid BEM, an efficient technique for modeling multi mode conversion of guided wave scattering problems. Time dependent wave forms are obtained through the inverse Fourier transformation of the numerical solutions in the frequency domain. 3D BEM program development is underway to model more practical ultrasonic wave signals. Some encouraging numerical results have recently been obtained in comparison with the analytical solutions for wave propagation in a bar subjected to time harmonic longitudinal excitation. It is expected that the presented modeling techniques for elastic wave propagation and scattering can be applied to establish quantitative nondestructive evaluation techniques in various ways.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.4
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• pp.343-351
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• 2016

Cryogenic spray characteristics of a nitrogen swirl injector operating in supercritical environment have been numerically investigated. By comparing the equation of states(EOS) used for supercritical condition, SRK EOS was applied to predict the nitrogen thermodynamic property under supercritical environment. A Chung's method was implemented for the calculation of viscosity and conductivity and Takahashi's correlation based on Fuller's Theorem was implemented for the calculation of diffusion coefficient. By injecting the nitrogen with 5 bar differential pressure into 50 bar chamber filled with nitrogen, numerical simulation has been conducted. The dynamic Smagorinsky sub-grid scale (SGS) model has been compared with the algebraic Smagorinsky SGS model using FFT frequency analysis. The instability at the liquid film and gas core inside injector and the propagation of pressure oscillation into the injector has been investigated. The spreading angle of swirl injector obtained by numerical calculation has been validated with experimental result.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.7
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• pp.552-561
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• 2016

In this experimental study, the dynamic stability derivatives of a tailless lambda-shape UAV are estimated from time history data of aerodynamic moments measured from the internal balance while the test model is forced to oscillate at given frequencies and amplitudes. A 3-axis forced oscillation apparatus is designed to induce decoupled roll, yaw, pitch oscillations respectively. The results show that the roll damping derivatives remain stable at the entire range of angle of attack tested, whereas the pitch damping derivatives become unstable beyond $15^{\circ}$ angle of attack. The amplitude and frequency have little impact on roll damping derivatives while the smaller amplitude and frequency of oscillation improves the pitch stability. The yaw damping derivative values are fairly small as expected for a tailless configuration. The results indicate that the proposed methodology and test apparatus area valid for estimating the dynamic stability derivatives of a tailless UAV.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.4
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• pp.326-335
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• 2014

Aerodynamic characteristics of the small two-stage turbo blower were investigated using commercial CFD tool(ANSYS CFX Ver. 14.5) in this paper. Turbo blower, which is a centrifugal type of turbomachinery, is used in various industries. It is used for application that required high static pressure rising at relatively small volumetric flow rate. In order to understand the mechanism of static pressure rising, the aerodynamic characteristics of the small two-stage turbo blower are analyzed at high rotating speed in this study. The k-${\omega}$ SST turbulence model, which is good at prediction of adverse pressure gradient flows, was applied. The CFD results of the turbo blower are validated by performance test. The static pressure rising of the turbo blower is nonlinearly increased over the first stage and the second stage. The secondary flow occurred at guide vanes, between the casing and the first impeller shroud, and the bottom of the impeller disk. As a result, It is required that whole fluid area is analyzed to predict aerodynamic characteristics of small two-stage turbo blower. and the result should be selected with considering for error from experiment and CFD.

• Science of Emotion and Sensibility
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• v.21 no.1
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• pp.165-176
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• 2018

A demand for user's participation in the designing process, which is called the participation design, is increasing with social change. Practically, however, there is lack of researches on the improvement of the problem in actual design development and participation design effect. In order to understand the field-based participation design effect in view of user's change of awareness on participation design, this study carried out a survey on the change of awareness through a design workshop in which all stakeholders have participated on the subject of agricultural direct sales facilities as a part of participation design programs. Many references were reviewed first to understand the participation design principles and their current research trend. Next, the questionnaire was developed using an effectiveness verification model for an effective analysis. A design workshop as one of the participation design programs was organized and applied for the field response. In order to analyze the effect, the survey on participants' change of awareness was carried out before and after the program. The survey questionnaires were about motivation, knowledge, recognition, function, and participation and asked the design study graduates. The participation design effect was supplemented by additional open questions. As a consequence, the participants in the participation design program showed the noticeable effect in knowledge and function about the agricultural direct sales facilities. It was found that they were also highly satisfied with the participation design result and they recognized an importance of collaboration. This study also showed that a sufficient time schedule considering agricultural village life should be given for a smooth operation of the program and also a working environment is necessary for designing work.

• 한국지형공간정보학회:학술대회논문집
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• 2004.10a
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• pp.141-146
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• 2004

최근 들어 국내에서도 홍수에 의한 재산과 인명피해를 최소화하기 위해 지역특성에 알맞은 홍수지도를 제작 중에 있으며, 주로 LiDAR를 이용하여 홍수지도 지형자료를 구축하고 있다. 그러나 이에 많은 시간과 비용이 소요되기 때문에 이미 전국적으로 구축된 수치지형도를 이용한 홍수지도 지형자료 구축의 가능성과 타당성을 검증의 필요성이 제기되고 있다. 이에 따라 본 연구에서는 수치지형도를 이용한 홍수지도제작시 가장 핵심이 되는 정확한 지형자료구축을 위해서 Breakline처리기법과 하천종횡단자료 연계방안을 중심으로 구리시 일부지역을 대상으로 DEM을 시범제작 하였다. 수치지형도와 LiDAR를 이용하여 구축한 DEM을 검수점을 통한 RMSE오차를 이용하여 수직위치정확도를 비교분석하였다. 분석을 위하여 선행연구(홍수지도제작, 2002)에서 검수점으로 사용한 9점과 제방부분의 실측한 9점을 본 연구의 검수점으로 사용하였다. 비교 결과 RMSE가 수치지형도 DEM의 경우 ${\pm}2.658m$이고, LiDAR DEM의 경우 ${\pm}3.430m$로 나타났다. 두 자료 모두 알려진 오차범위보다 훨씬 높은 오차가 발생함을 알 수 있었다. 향후 수치지형도를 이용한 효율적인 홍수지도 지형자료 구축을 위해서는 수치지형도의 신속하고 지속적인 갱신이 필요할 것이며, 현재 도시지역에만 구축되어 있는 1:1,000 수치지형도를 주변 하천지역까지 확대해서 구축해야 할 필요성이 있을 것으로 사료된다. 아울러 도입초기단계의 LiDAR 측량기술의 보급과 관련모델의 기술의 발달로 인하여 정확도 높은 DEM이 요구된다면 고밀도의 방대한 양의 LiDAR 자료로 DEM을 구축하는 것이 바람직하다고 사료된다.및 이용대책을 수립하는 데 활용될 수 있다., $1,000-2,000{\mu}g\;g^{-1}$), 나머지 177종 식물은 살초활성을 나타내지 않았다. 높은 살초활성을 나타낸 식물로부터 분리되는 천연활성물질들은 향후 새로운 제초제 개발을 위한 모화합물 제공, 상호대립억제 작용성을 갖는 작물 품종 개발 혹은 개량에의 활용, 그리고 친환경 유기농업용 잡초방제에의 활용이 기대된다.내(皮膚上皮組織內)의 Langerhans cell내(內)의 Birbeck granule에 비(比)해 수적(數的)으로 현저히 감소(減少)되어 있었다. 그러나 Thy-1 양성(陽性) dendritic cell에서 볼 수 있는 dense-core 과립(顆粒)은 별변화(別變化)없이 쉽게 관찰(觀察)될 수 있었다. 조직배양(組織培養)을 한 견(犬)의 keratinocyte에 대(對)해 사람 pemphigus vulgaris의 항체(抗體)로 반응(反應)시킨 후 protein-A gold(15 nm)로 표식(標識)시킨 바 제일 바깥 상층(上層)의 keratinocyte에 있어서 세포막표면(細胞膜表面)을 따라 표식(標識)되어 세포막항원(細胞膜抗元)을 나타내었으며, 이와 같은 소견(所見)으로 미루어 정상피부(正常皮膚) 중층편평상피세포(重層扁平上皮細胞)에서도 동일(同一)한 소견(所見)을 관찰(觀察)할 수 있다고 본다.al remnants, Resorption of fetus로 관찰된 것이다. Fetal death는 수정후 $14{\sim}18$일까지의 사망으로써 Maceration of fetus로 관찰되는 것이다. 통계학적 분석은 각 Group의 착상 을과 자궁 내 사망 율을 산출할 때에는 각 임신마우스에 따라 발생빈도가 크

• Informatization Policy
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• v.26 no.4
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• pp.36-61
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• 2019

While smart devices can have a positive impact on work efficiency and productivity by reducing time-space constraints and enabling rapid processing of tasks, side effects can arise from the imbalances between work and personal life. In recent years, as smart devices are increasingly used in work environments, it is more necessary than ever to understand the related phenomenon, find the cause of negative effects, and search for appropriate solutions. This study has developed and verified a theoretical model that shows how the technical characteristics known as the utility of smart devices are converted into negative results such as work-life conflict. As a result of analyzing the collected data from the employees, our study provides significant implications for the researchers, as well as the practitioners and policy makers, regarding various relationships among IT-enabled work flexibility, after-hours work connectivity and work-life conflict, and the new knowledge about the important role of segmentation supplies from the organization.

• The Journal of the Acoustical Society of Korea
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• v.32 no.2
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• pp.95-103
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• 2013

An underwater acoustic (UWA) communication in shallow water is strongly affected by the water surface and the seabed acoustical properties. Every reflected signal to receiver experiences a time-variant scattering in sea surface roughness and a grazing-angle-dependent reflection loss in bottom. Consequently, the performance of UWA communication systems is degraded, and high-speed digital communication is disrupted. If there is a dominant signal path such as a direct path, the received signal is modeled statistically as Rice fading but if not, it is modeled as Rayleigh fading. However, it has been known to be very difficult to reproduce the statistical estimation by real experimental evaluation in the sea. To give an insight for this scattering and grazing-angle-dependent bottom reflection loss effect in UWA communication, authors conduct experiments to quantify these effects. The image is transmitted using binary frequency shift keying (BFSK) modulation. The quality of the received image is shown to be affected by water surface scattering and grazing-angle-dependent bottom reflection loss. The analysis is based on the transmitter to receiver range and the receiver depth dependent image quality and bit error rate (BER). The results show that the received image quality is highly dependent on the transmitter-receiver range and receiver depth which characterizes the channel coherence bandwidth.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.2
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• pp.177-183
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• 2005

The effluent quality is directly affected by the separation of biological solids in a final clarifier because the majority of discharged $BOD_5$ and SS are virtually dependent on the results of biological solids in the sedimentation tank effluent. If a final clarifier is effectively designed and operated, the desired goal of clarification for wastewater can be achieved together with the cost reduction in the treatment of wastewater. To this end flow characteristics and the removal efficiency of SS are numerically investigated especially by the change of the inlet position and the installation of baffle to improve the performance of a rectangular final clarifier. The 2-D computer program developed in a rectangular coordinates has been successfully validated against experimental residence time distribution(RTD) curves obtained by tracing radio-isotope. The lowering of the inlet position weakens the density current and induces the settling of SS in the front zone of a clarifier. Thus the decreased traveling distance of the sludge increases the removal efficiency of SS in the effluent. The inlet baffle installed in the front region of clarifier prevents the short circuiting flow and induces to flow into the dense underflow, which eventually improves the effluent quality. In the case of lower inlet position, however, installation of baffle results in degradation of effluent quality. Consequently it is strongly recommended that in-depth numerical study be performed in advance for optimizing a clarifier design and retrofitting to improve effluent quality in a final clarifier.

• Journal of the Earthquake Engineering Society of Korea
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• v.16 no.2
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• pp.47-60
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• 2012

Based on the Korean Building Standard Law, a building less than 3-stories and $1000m^2$ in area is defined as a small-level building and, as a result, this type of building has been excluded from the requirement to comply with seismic design. In order to prevent the loss of life and property under earthquake loadings, the small-scale building should satisfy the seismic performance specified in the current code through a seismic retrofit. In this study, a seismic retrofit scheme of a Buckling-Restrained Knee Brace (BRKB) was developed for non-seismic 2-story steel buildings, including small-scale buildings, using a fragility contour method. In order to develop an effective retrofit scheme of the BRKB for the building, a total of 75 BRKB analytical models were used to achieve the desired performance levels and analyzed using the fragility contour method. The seismic performance of the retrofitted building was evaluated in terms of the weight of the developed BRKB systems. This study shows that the fragility contour method can be used for rapid evaluation and is an effective tool for structural engineers.